Pierre Poilievre, the man who is the favorite to become Canada’s next leader, has painted his country as “broken” and ridden with “crime and chaos.” He has derided Prime Minister Justin Trudeau as a “wacko” and his ministers as “crazy,’’ “disastrous,” “incompetent and discredited.”

In Parliament, he called a leftist opposition leader and former Trudeau supporter “a fake, a phony and a fraud’’ and a “sellout.’’ Enraged, the leader stood up from his seat, walked into the aisle, and yelled, “I’m right here, bro.”

“Do it,” Mr. Poilievre shot back as the House speaker struggled to restore calm and pleaded that lawmakers respect “the rules that we have.”

Mr. Poilievre, 45, the opposition Conservative Party leader, has been stretching the rules in Canada’s political discourse with a combative, attack-driven style and an anti-elite, populist message that has been described as authentic by supporters and Trumpian by critics.

So far, it’s worked.

For the past year, Mr. Poilievre and his party have enjoyed a double-digit lead in the polls over Mr. Trudeau and his Liberal Party. If the polls hold, Mr. Poilievre will emerge as the next prime minister in a general election that must be held by October but will most likely be held in the spring after Mr. Trudeau’s announcement on Monday that he would resign as party leader and prime minister once his party decides on a successor.

A career politician long known as a fierce attack-dog for his party, with an instinctive sense of the themes that resonate among voters, Mr. Poilievre has successfully pummeled the unpopular Mr. Trudeau in the past year and made him appear out of touch.

Mr. Poilievre drove the nation’s political agenda by handpicking issues — housing costs, inflation and immigration — that, according to many Canadians, Mr. Trudeau’s government had underestimated or mishandled.

But in a news conference announcing his resignation, Mr. Trudeau said that Mr. Poilievre’s “vision for this country is not the right one for Canadians,” adding that the opposition leader was not offering “an ambitious, optimistic view of the future.”

Whether Mr. Poilievre can cling to his lead in the polls, or even build on it, as voters now get to know him better remains unclear. In the months ahead, the Liberal Party’s choice of a successor could yield a bump in the party’s popularity. And Mr. Poilievre, who became leader of the Conservatives in 2022, will have to campaign on his own agenda to win over mainstream voters.

“He’d be very different from any other prime minister we’ve had,” said Duane Bratt, a political scientist at Mount Royal University in Calgary, Alberta. “He’s been very combative, and he’s been like that his whole life. That’s great as an opposition leader, and even as a junior minister. But can he do that as prime minister?”

Like other populist leaders, Mr. Poilievre has tapped into the post-pandemic frustrations of voters over rising living costs, unaffordable housing and what to many seemed like a smug Trudeau government that made big decisions — like increasing immigration to historical levels or imposing a carbon tax — without much explanation or consultation.

Three years ago, Mr. Poilievre was one of the few politicians to openly support truckers who paralyzed the center of Ottawa, the capital, for weeks to protest vaccine mandates.

“He’s channeled an anti-elitism in Canada,” said Lori Turnbull, a political scientist at Dalhousie University in Halifax, Nova Scotia. “It is populist, it is anti-institutional. That is a big part of his messaging.”

Mr. Poilievre has pushed a traditionally conservative message of personal freedom, small government, lower taxes, being tough on crime and softer on regulations on Canada’s oil industry.

But he has laced his message with railings against “globalist Davos elites,” threatening to fire Canada’s central banker, embracing cryptocurrency and attacking the mainstream media, especially the public broadcaster, the C.B.C., which he has vowed to defund.

“The problem we’ve had in this country and in all of the countries that have been afflicted by this horrendous utopian wokeism is that it’s been focused on the grand, the grandiosity of the leadership of the egotistical personalities on top and not the things that are grand and great about the common people,” Mr. Poilievre said in a recent interview with Jordan Peterson, the Canadian psychologist and conservative social media star.

“And that is another reason why I think we’re doing very well,” Mr. Poilievre added. “People are saying, finally, there’s someone who’s focused on letting me take back control of my own life.’’

Elon Musk, the billionaire and one of President-elect Donald J. Trump’s most influential supporters, said “great interview” about Mr. Poilievre’s appearance on Mr. Peterson’s podcast. Mr. Musk appeared to embrace Mr. Poilievre even as he continued to belittle Mr. Trudeau.

“Girl, you’re not the governor of Canada anymore, so doesn’t matter what you say,” Mr. Musk posted on social media after Mr. Trudeau said there was not “a snowball’s chance in hell” that Canada would become part of the United States, as Mr. Trump has suggested.

In his personal life, Mr. Poilievre couldn’t be more different from Mr. Trudeau, who — as the son of Pierre Trudeau, who led Canada for nearly 16 years and helped define Canada’s modern identity — grew up in the prime minister’s official residence in Ottawa.

In an apparent effort to emphasize his modest origins, Mr. Poilievre has often told the story of how he was born in Calgary to a 16-year-old mother and given up for adoption. His adoptive parents were schoolteachers who separated when he was 12, after which his father came out as gay.

When he was elected Conservative Party leader in a landslide in 2022, he saluted his biological mother, his adoptive parents and his father’s longtime partner, all of whom were in the audience.

“We’re a complicated and mixed-up bunch, like most families, like our country,” said Mr. Poilievre, who supports same-sex marriage and abortion rights.

Mr. Poilievre has two young children with his wife, Anaida Galindo, a former Senate aide he met in Ottawa. Ms. Poilievre was born in Venezuela but grew up with her family in Montreal. Her husband has often referred to the benefits of immigration by citing as an example Ms. Poilievre’s family, saying they came to Canada “with almost nothing’’ and “like so many immigrant families, built our country.”

Involved in conservative politics in Calgary since his early teens, Mr. Poilievre became the youngest member of Parliament when he was elected in 2004 at the age of 25. He rose quickly through the ranks, impressing older politicians with his hard work, acumen and combativeness, earning the nickname “Skippy.”

He tried to shed the image evoked by the nickname with a makeover in the summer of 2023. Abandoning navy blue suits and ties, he began appearing in public in jeans and sometimes tightfitting T-shirts. He jettisoned his squarish glasses for contacts and aviator sunglasses.

“He’s transformed his own image from this nerdy little guy with the glasses and scowl on his face all the time to this sort of Bitcoin bro who is appealing to young voters, male voters,” said Ms. Turnbull, the political scientist.

Mr. Poilievre said in the interview with Mr. Peterson that he had become “tougher” since becoming Conservative leader and was ready to become prime minister.

“It’s personal for me,” he said. “I don’t come from a privileged or wealthy background. I was adopted by schoolteachers, grew up in a normal suburban neighborhood. We didn’t always have money. But I was able to get here.”

Just weeks after Russia invaded Ukraine in February 2022, Ukrainian troops began running out of ammunition for their aging Soviet-era artillery.

The United States was soon scouring foreign arsenals around the globe for the right kinds of shells as part of its pledge to support Kyiv against its much better equipped adversary. But the Pentagon knew it would never be able to get enough, as fewer nations made Russian heavy artillery ammunition and many Cold War stockpiles of them had become unusable with age.

So on a Saturday that spring, Defense Secretary Lloyd J. Austin III called Gen. Mark A. Milley, his chairman of the Joint Chiefs of Staff at the time, to figure out how many American howitzers could be quickly shipped to Ukraine along with newly made high-explosive shells.

That call set into motion a chain of events that led to a pipeline of arms for Ukraine, and a reshaping of how the United States envisions building alliances as it pushes back on Russia’s influence.

Officials in the Biden administration turned first to U.S. allies for help. But they also drew on relationships developed over years with the militaries of non-NATO countries to build a network to aid Ukraine, something the administration considers a shining example of how its focus on strengthening alliances has paid dividends to U.S. interests around the world.

On Thursday, the collective of nations, known as the Ukraine Defense Contact Group, is gathering at Ramstein Air Base in Germany for the 25th and final time under the Biden administration.

Whether it continues under the incoming administration’s leadership is uncertain. President-elect Donald J. Trump is deeply skeptical of supporting Ukraine, puts much less stock in alliances and has openly curried favor with President Vladimir V. Putin of Russia.

When the contact group first met on April 26, 2022, just 61 days after Russia invaded, the United States, Britain, France and a handful of other nations had been supporting Kyiv individually. But dozens more joined them in Germany to hear a battlefield update directly from their Ukrainian counterparts.

The massacre of civilians in Bucha, a Kyiv suburb, had recently come to light. Mr. Austin and General Milley made it clear that similar atrocities were likely to happen without more arms and ammunition for Ukraine, and asked the assembled dignitaries to dig deep into their arsenals for desperately needed supplies.

The meeting was put together quickly, on just four days’ notice at Ramstein, chosen for its central location in Europe, its long runway for delegations arriving by plane and the ability to maintain tight security while hosting sensitive discussions about Ukraine’s future.

In a nondescript ballroom at the base’s officers’ club, Mr. Austin and General Milley, flanked by their Ukrainian and German counterparts, sat at the head of a horseshoe arrangement of folding tables alongside representatives from 40 countries.

It has since grown to at least 53 countries, and the Pentagon has hinted that others have kept their participation secret.

They have met roughly every month since.

“Putin’s war is a challenge to free people everywhere, and we all have a stake in ensuring that autocrats cannot place their imperial ambitions ahead of the bedrock rights of free and sovereign peoples,” Mr. Austin said in his opening remarks on Thursday. “Ukraine is waging a just war of self-defense. And it is one of the great causes of our time.”

A global battle for arms and influence

Shortly after Mr. Austin landed at Ramstein in a C-17 cargo plane on Wednesday morning, snow began falling on hulking Air Force transport jets along the runway. He prepared for the next day’s meeting in a nearby hotel on base.

It would be the final contact group meeting of his tenure as defense secretary.

That evening, the Ukrainian defense minister, Rustem Umerov, and two aides walked the halls of the hotel’s second floor in military fatigues to join a private meeting with Mr. Austin.

The Ukrainians traveled light, without the sort of large security detail that hovered nearby for his American counterpart.

The troops Mr. Umerov leads in some ways still straddle the two defining military cultures of the Cold War — that of the U.S. and NATO, and that of the former Soviet Union.

Over decades, the two sides created their own ecosystems of arms that were compatible with those of allies, but not with those of their foes. And while the differences between the 152-millimeter shells fired by Russian-made artillery pieces and the 155-millimeter version adopted by NATO may seem small, they are emblematic of how militaries around the world have long been divided into one of two camps.

Determining whether a country was aligned with the West or with Moscow was often as easy as spotting which weapons it used.

But the number of countries manufacturing Russian-designed weapons has dwindled, especially as many former Soviet republics that once produced them have since joined NATO.

Global supplies of those arms have been further reduced as Russia has paused much of its arms exports to maintain sufficient ammunition supplies for its own needs in Ukraine.

The change has left many of Russia’s traditional clients looking elsewhere for ordnance just as more countries around the world have begun producing NATO-standard weapons — even if they are not formal members of the alliance.

A new type of alliance is born

The conversion of Ukraine — a former member of the Soviet Union — over to NATO warplanes like F-16s and arms like HIMARS mobile rocket launchers has pulled even more countries away from Russia’s orbit.

That shift is evident in the makeup of the contact group itself, which contains 20 nations formerly in Moscow’s Cold War sphere of influence — some of which continued to purchase Russian arms until the invasion of Ukraine.

The contact group’s composition shows a novel approach for American power projection — one that U.S. officials have said future administrations could use in case of major conflicts, such as a potential Chinese attack on Taiwan.

While NATO has always been an alliance of nations who have pledged to come to each others’ aid if attacked, its influence has expanded far beyond its formal membership of 32 nations through partnerships with dozens of other countries since the mid-1990s. The United States leveraged that network in creating the contact group.

In addition to the NATO member states, many of the countries that participate in the contact group are what the State Department calls “major non-NATO allies.” They include Argentina, Australia, Colombia, Israel, Japan, Kenya, Morocco, New Zealand, Qatar, South Korea and Tunisia.

After decades of arms sales, these countries collectively had a deep inventory of NATO-standard arms to share with Ukraine.

Others are on NATO’s periphery, with Bosnia, Georgia, Ireland, Kosovo and Moldova joining the group as well as Ecuador and Peru, two former Russian military clients that have entered into partnerships with the alliance.

Lessons from the battle against ISIS

Mr. Austin modeled the contact group on the Coalition to Defeat the Islamic State, which formed in September 2014 and came to encompass more than 80 nations.

At that time, Mr. Austin was an Army general in charge of U.S. forces in the Middle East. Eight years later in Ramstein, he shook the hands of many of the same leaders who had supported him in uniform.

Together, the nations of the group supporting Ukraine have supplied Kyiv with more than $126 billion in military aid, funding and hardware, according to the Pentagon.

While the defense secretary worked on growing and organizing the new coalition, the State Department worked behind the scenes to get even more of Russia’s former military client states to donate their Soviet-era arms to Kyiv in exchange for financial grants and expedited access to the latest American weaponry.

Two and a half years into the war, a Defense Department office still updates a file every week called The Matrix — a spreadsheet of the countries known to have Russian weapons along with their likely inventories.

It also includes what the United States is prepared to ask them for on Ukraine’s behalf, and a list of incentives Washington can offer in exchange thanks to an influx of money authorized by Congress.

Whether such efforts continue under the next administration is unknown, but it is clear that military and civilian officials have considered the possibility that Ukraine may have to fight on without its single biggest benefactor.

Should the Trump administration decide to leave the Ukraine Defense Contact Group, Pentagon officials have said, another country could take up the U.S. leadership role, continuing the global effort to supply arms to Ukraine without Washington’s influence.

Elon Musk is not just dabbling in German politics. He is attempting to break a political blockade that has kept the nation’s most prominent far-right party out of government even as it has gained strength with voters.

Mr. Musk will be the host of a live interview on Thursday with Alice Weidel, who is the chancellor candidate for that party, the Alternative for Germany, known as the AfD, in the country’s snap election scheduled for Feb. 23. The event, on X, the social media platform that Mr. Musk owns, has raised alarms and threats of legal consequences among Germany’s political class.

That is, in large part, because Mr. Musk is offering the AfD a level of publicity and legitimacy that it has long been denied in German public life.

The AfD has risen to the second position in German national polls, backed by about a fifth of the electorate. It has gained support with an unwavering anti-establishment campaign, which rails against the millions of migrants and refugees who have entered the country over the last decade from the Middle East and Ukraine.

Parties with similar immigration messages elsewhere in Europe, like the Brothers of Italy and Austria’s Freedom Party, have risen to federal power. But in Germany, still haunted by its Nazi past, no other party will work with the AfD. Its candidates complain they receive far less airtime than other candidates on the nation’s political talk shows.

At the same time, the AfD has made forays into language and actions German leaders deem extreme. The party has been forced to expel members for using racist and antisemitic language. One of its leaders has been repeatedly penalized by German courts for repeating banned Nazi slogans.

The party is under observation by domestic intelligence. Three of its state chapters as well as its entire youth wing are classified as confirmed right-extremist, a designation that intelligence services make after extensive observation. More than 100 employees working for AfD members of Parliament are also confirmed right extremists, according to an investigation by a public broadcaster.

In a 2016 speech, with the AfD gaining steam before federal elections, former Chancellor Angela Merkel urged all German parties to unite against the AfD. It was, she said, not just a problem for her own conservative party but “a challenge for all of us gathered in this house.”

The anti-AfD collective has not broken since. Not after the party climbed in the polls and won victories in major state elections last year, and not after it tried to put a more moderate face forward as its chancellor candidate: Ms. Weidel, a former investment banker who lives with her Sri Lankan same-sex partner and their children in Switzerland.

Enter Mr. Musk, who controls a powerful media platform that is increasingly populated with right-wing influencers. He has become a close confidant of President-elect Donald J. Trump and in online posts has begun promoting far-right candidates and parties across Europe.

In December, Mr. Musk reposted a video from Naomi Seibt, a 24-year-old German conservative social media star who has gained a large following on X and on YouTube, through her harsh criticisms of climate scientists and efforts to combat global warming. She is also close with the AfD, and appears to have helped sway Mr. Musk to support the party.

“Only the AfD can save Germany,” Mr. Musk wrote, in his post, which included one of her videos.

Ms. Weidel welcomed the support. “You are perfectly right, @elonmusk!” she wrote in response.

Mr. Musk has since written an opinion piece in the German newspaper Die Welt expounding on his support for the party, which he called the “last spark of hope” for Germany. In it, he cast the AfD not as extreme, but as a reasonable alternative to a calcified political establishment.

“The portrayal of the AfD as far-right is clearly wrong considering that Alice Weidel, the leader of the party, has a same-sex partner from Sri Lanka! Does that sound like Hitler to you? Come on!” he wrote.

On Thursday evening in Germany, Mr. Musk will go even further, playing host to Ms. Weidel in an X “Spaces” conversation, akin to one he held with Mr. Trump last summer.

Mr. Musk, and many of his X users, are fascinated with European right-wing political parties like the AfD. But in many ways the party’s positions diverge from Mr. Musk’s personal and business views — and his role as an adviser to Mr. Trump.

The AfD has famously fought back against the construction of a factory in Germany for Tesla, the electric car company also run by Mr. Musk. In an interview with The American Conservative this week, Ms. Weidel praised Mr. Trump, but she suggested that Germans have become “slaves” to the United States, including aiding America in wars over the last 30 years.

“We Germans have lived in this situation for a long time, definitely to the advantage of the U.S.,” she said.

The European Commission has said it will examine Mr. Musk’s interference in European politics given his enormous power through his ownership of X and his close ties, however impermanent they may turn out to be, to the incoming American president.

Europe’s center-left political parties — Germany’s Social Democrats among them — have jointly released a statement urging Brussels to use “all the legal means available” to protect democracy against misinformation and foreign interference on social media.

Gérard Araud, an outspoken former French ambassador to Washington, has doubts about Europe’s ability to keep its unity in withstanding attacks from Mr. Musk on incumbent leaders.

“Europeans, for whom the relationship with the United States is civilizational and existential, are paralyzed by the increasingly incendiary statements of Trump and Musk,” Mr. Araud wrote on X. “They hope that these are just words.”

German leaders have alternately criticized Mr. Musk and tried to ignore him. In an interview this week, Chancellor Olaf Scholz dismissed the billionaire’s efforts to sway German voters. “I do not believe in courting Mr. Musk’s favor,” he said. When dealing with social media posts, he added in English, his rule is, “Don’t feed the troll.”

German voters also appear unswayed, at least for now. Three quarters of respondents to a German broadcaster’s poll said it was inappropriate for Mr. Musk to comment on German politics.

But the same poll showed a majority of respondents believed that Mr. Musk’s efforts would help the AfD in the election.

Steven Erlanger and Christopher F. Schuetze contributed reporting.