Those goals put Trump and Ryan increasingly at odds over both tone and substance as the businessman barrels toward the GOP presidential nomination. While Ryan is appealing for political civility and a party rooted in traditional conservative principles, Trump is bucking campaign decorum and embracing policy positions that are sharply at odds with years of GOP orthodoxy.

Their starkly different visions for the Republican Party are a microcosm of the broader fissures roiling the GOP. And if Trump does become the Republican nominee, he and the House speaker’s ability to work together could be the first test of whether a party in this much turmoil can stay together.

“Trump’s obviously running on issues that are contrary to conservatives and at odds with what a lot of what Paul Ryan believes,” said Peter Wehner, a former adviser to President George W. Bush.

For now, Trump and Ryan are engaged largely in a cold war, with the politicians only occasionally mentioning each other by name. Ryan has picked key moments to draw implicit contrasts with Trump, including condemning the billionaire’s refusal to take responsibility for violence at his rallies. Trump will launch the next volley Tuesday when he campaigns in Ryan’s hometown of Janesville, Wisconsin, ahead of the state’s April 5 primary.

Trump, in his trademark contradictory style, has both praised Ryan and ominously warned the speaker against crossing him.

“Paul Ryan, I don’t know him well, but I’m sure I’m going to get along with him, and if I don’t, he’s going to have to pay a big price, OK?” Trump said after his victories on Super Tuesday. A week later, after speaking with Ryan by phone, Trump said of the speaker: “I like him a lot. I respect him a lot.”

People close to Ryan say the Wisconsin lawmaker is in disbelief about Trump’s staying power. While he’s publicly vowed to support whomever his party nominates, Ryan has privately said he’s focused on trying to keep the GOP’s House majority this fall and on fundraising for the party — leaving some friends with the impression that he would be a less-than-enthusiastic Trump backer in a general election.

Looming large are Ryan’s own political ambitions. He passed on running for the White House in 2016, but some Republicans still harbor hopes that he could emerge as the nominee in a convention fight this summer if neither Trump nor Ted Cruz clinch the nomination by then.

“I would be less than honest with you if I said people are not mentioning a Ryan candidacy from time to time,” said Rep. Charlie Dent, a Pennsylvania Republican who meets regularly with Ryan. “Clearly there are many in Congress who see Paul Ryan as a consensus candidate.”

Ryan has vigorously denied that he’s interested, though he was similarly definitive last year when he rebuffed calls to run for the speaker’s job. He’s also insists that his role as chairman of the July convention requires him to remain officially neutral despite his obvious displeasure with Trump.

Yet Ryan’s refusal to fully disavow Trump has left him open to criticism that he either cares too much about keeping the real estate mogul’s enthusiastic supporters in the Republican fold or that he doesn’t fully understand the threat.

“The barbarian is at the gate, and Paul Ryan wants to talk sense to him?” wrote David D. Haynes, the editorial page editor of the Milwaukee Journal Sentinel, the largest newspaper in Ryan’s home state.

Trump, in private at least, has tried to soften such dire talk. A few weeks ago, he sent Ryan a copy of a Washington Post article that he’d marked up to show his disagreement with the piece’s assertion that he was a threat to GOP orthodoxy. A Ryan aide confirmed that Trump sent the article, speaking on condition of anonymity because the aide was not authorized to speak publicly by name.

Ryan has been working behind the scenes to produce congressional plans on issues including health care, the economy and national security. Though not the original intent of Ryan’s “agenda project,” the effort could give Republicans something to run on if they can’t or don’t want to hitch themselves to their presidential nominee.

Trump’s own policy proposals, though often vague, have sometimes sharply conflicted with where Ryan is trying to position the party, particularly on economic issues.

Ryan rose to prominence among Republicans for spending proposals that eventually would privatize government entitlement programs, gradually reducing those operations’ share of federal spending. While Trump has joined Republicans in bemoaning alleged abuses of entitlement programs, he’s long blasted proposals like Ryan’s.

“As Republicans, if you think you are going to change very substantially for the worse Medicare, Medicaid and Social Security in any substantial way, and at the same time you think you are going to win elections, it just really is not going to happen,” Trump said during a 2013 appearance at the Conservative Political Action Conference.

Trump has also spent decades criticizing U.S. trade policy and advocating steep tariffs on Chinese imports. It’s a protectionist argument that puts him at odds with decades of Republican support for international trade, though he’s in line with a growing contingent of House Republicans who see sweeping foreign trade deals as detrimental to American workers.

Before becoming speaker, Ryan was among the most vocal House Republicans in backing trade agreements, including President Barack Obama’s Asia-Pacific pact. As speaker, Ryan has yet to schedule a vote on the Pacific Rim deal, saying he and other members are carefully vetting the details.