House Speaker Paul Ryan seems confident that a Republican Congress can rein Donald Trump in, but Trump has already forced changes to the Party’s stance on Vladimir Putin’s Russia. PHOTOGRAPH BY PHILIP MONTGOMERY FOR THE NEW YORKER

One of the main arguments made by prominent Republicans who have refused to back Donald Trump is that endorsing the candidate means embracing everything he stands for and says.

“You own his politics. You own his policies, even the ones that only last as long as the next contradiction,” Rick Wilson, the fiercely anti-Trump Republican strategist, wrote in an open letter to Republicans last month.

The retort from many Trump-backing officials, some of whom privately despise their candidate, is that a Republican Congress could control a President Trump. This was House Speaker Paul Ryan’s theory when he reluctantly endorsed the Republican nominee. Even though Trump’s policy agenda is the opposite of Ryan’s on trade, immigration, entitlements, and other issues, Ryan and others hope that Trump’s lack of interest in policy details and his appetite for winning would make him a rubber stamp for the Ryan agenda. As Ryan put it when he endorsed Trump, back in June, “For me, it’s a question of how to move ahead on the ideas that I—and my House colleagues—have invested so much in through the years.”

When it comes to domestic policy, the Republican Convention last week offered something of a draw in the battle between the Ryan and Trump agendas. Ryan barely mentioned Trump in his speech to delegates in Cleveland, as he made a case for a more traditional Republican agenda of low taxes and less regulation. Interestingly, Donald Trump, Jr., echoed many of Ryan’s themes in his speech, rather than the working-class populism of his father. Trump’s own speech, with its apocalyptic rhetoric about “poverty and violence at home, war and destruction abroad,” was almost completely empty of policy proposals, which gives some credence to Ryan’s argument that he and his colleagues will be able to fill such a vacuum.

But, after almost two weeks of Conventions, there is one area of Republican foreign policy that Trump has completely reinvented in his image: the Party’s posture toward Russia. There is almost no issue on which Trump has been more consistent than his interest in strengthening ties with Vladimir Putin and clearing away the obstacles that have hindered the U.S.-Russia relationship.

The profound changes started two weeks ago, during the drafting of the official Republican platform. The Trump campaign remains skeletal, and it did not take an active interest in many aspects of the drafting process. The one area where Trump’s aides were extremely active was in the Party’s position on Ukraine and Russia. For years now, the consensus view among senior Republicans has been that the United States should provide lethal aid to the Ukrainian government, which since 2014 has been under constant harassment by Russian-backed separatist forces. As first reported by Josh Rogin, in the Washington Post, Trump’s aides scuttled language from the platform backing U.S. military assistance to Ukraine. (The Obama Administration happens to have a no-arms stance, making this one of the only aspects of Obama’s foreign policy that Republicans have chosen to embrace.)

It was conceivable that the change to the Party platform was an isolated event and not one that represented a Republican turn away from our European allies and toward Moscow. But then Trump made an even more jaw-dropping policy announcement: he told the Times that he would not necessarily defend NATO countries if they were attacked by Russia. Yesterday, after WikiLeaks released Democratic National Committee e-mails, which officials have said were likely obtained by Russia, Trump went even further. At his bizarre press conference, the candidate was repeatedly asked about policy on Russia and his relationship with Russia.

The press understandably has been focussed on Trump’s casual plea for Russia to hack Hillary Clinton’s e-mails. As frightening as that comment was—it was like watching Nixon publicly ask the burglars to go back in and find more files at the Watergate—Trump’s other remarks about Russia yesterday may have been more revealing of his actual policy views.

“I would like to know, if you became President, would you recognize Crimea as Russian territory?” one reporter asked. “And also if the U.S. would lift sanctions.” Trump, without hesitation, responded, “We’ll be looking at that. Yeah, we’ll be looking.”

Crimea, a Ukrainian territory, was seized by Russia two years ago. The United Nations General Assembly, in a hundred-to-eleven vote, has called on countries not to recognize Crimea as part of Russia. Some prominent Republicans, including John McCain, were willing to go to war with Russia to defend the territory. Trump suggested that he might well let Putin have it.

At this week’s Democratic Convention, several former high-ranking officials have seized on Trump’s pro-Putin stance. Madeleine Albright, the Secretary of State under Bill Clinton, said, “The truth is that a Trump victory in November would be a gift to Vladimir Putin.” Last night, Leon Panetta, Obama’s former C.I.A. director and Secretary of Defense, was incredulous over Trump’s hacking request. “Today, Donald Trump once again took Russia’s side,” Panetta said. “He asked the Russians to interfere in American politics. Think about that for a moment. Donald Trump is asking one of our adversaries to engage in hacking or intelligence efforts against the United States to affect our election.”

Democrats have largely taken the position that Trump is an unwitting agent of Putin—a “useful idiot,” in the language of the Cold War. It’s surprising, as my colleague Jane Mayer has noted, that they have not been more aggressive. What is more shocking is that Republicans have largely remained silent. In a matter of weeks, Trump has made the G.O.P. a pro-Putin party. If he is President, there will be little that a Republican Congress can do to stop Trump’s embrace of Russia.