The long decline of the Republican Partys internationalist wing may have reached a tipping point.

Since Donald Trump emerged as the GOPs dominant figure in 2016, he has championed an isolationist and nationalist agenda that is dubious of international alliances, scornful of free trade, and hostile to not only illegal but also legal immigration. His four years in the White House marked a shift in the partys internal balance of power away from the internationalist perspective that had dominated every Republican presidency from Dwight Eisenhower through George W. Bush.

But even so, during Trumps four years in office, a substantial remnant of traditionally internationalist Republicans in Congress and in the key national-security positions of his own administration resisted his efforts to unravel Americas traditional alliances.

Now though, evidence is rapidly accumulating on multiple fronts that the internal GOP resistance is crumbling to Trumps determination to steer America away from its traditional role as a global leader.

In Congress, that shift was evident in last weeks widespread Senate and House Republican opposition to continued aid for Ukraine. The same movement is occurring among Republican voters, as a new Chicago Council on Global Affairs study demonstrates.

The study used the councils annual national surveys of American attitudes about foreign affairs to examine the evolution of thinking within the GOP on key international issues. It divided Republicans into two roughly equal groups: those who said they held a very favorable view of Trump and the slightly larger group that viewed him either only somewhat favorably or unfavorably.

The analysis found that skepticism of international engagementand in particular resistance to supporting Ukraine in its grueling war against Russiais growing across the GOP. But it also found that the Republicans most sympathetic to Trump have moved most sharply away from support for an engaged American role. Now a clear majority of those Trump-favorable Republicans reject an active American role in world affairs, the study found.

Trumpism is the dominant tendency in Republican foreign policy and its isolationist, its unilateralist, its amoral, Richard Haass, a former president of the Council on Foreign Relations and the director of policy planning at the State Department under George W. Bush, told me a few months ago.

That dynamic has big implications for a second Trump term. The growing tendency of Republican voters and elected officials alike to embrace Trumps nationalist vision means that a reelected Trump would face much less internal opposition than he did in his first term if he moves to actually extract America from NATO, reduce the presence of U.S. troops in Europe and Asia, coddle Russian President Vladimir Putin, or impose sweeping tariffs on imports.

During Trumps first term, the party was not yet prepared to abandon internationalism and therefore opposed him, Ivo Daalder, the chief executive officer of the Chicago Council, told me. On Russia sanctions, on NATO, on other issues, he had people in the government who undermined him consistently. That wont happen in a second term. In a second term, his views are clear: He will only appoint people who agree with them, and he has cowed the entire Republican Party.

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The erosion of GOP resistance to Trumps approach has been dramatically underscored in just the past few days. Most Senate Republicans last week voted against the $95 billion aid package to Ukraine, Israel, and Taiwan. After that bill passed the Senate anyway, Republican House Speaker Mike Johnson said that he would not bring it to a vote. All of this unfolded as an array of GOP leaders defended Trump for his remarks at a rally in South Carolina last weekend when he again expressed disdain for NATO and said he would encourage Russia to do whatever the hell they want to members of the alliance who dont spend enough on their own defense.

Many of the 22 GOP Republicans who voted for the aid package for Ukraine, Israel, and Taiwan were veteran senators whose views about Americas international role were shaped under the presidencies of Ronald Reagan, George H. W. Bush, or George W. Bush, long before Trump and his America First movement loomed so large in conservative politics. It was telling that Senate Republican Leader Mitch McConnell, who was first elected to the Senate while Reagan was president in 1984, was the aid packages most ardent GOP supporter.

By contrast, many of the 26 Republican senators who voted no were newer members, elected since Trump became the partys leading man. Republican Senator J. D. Vance of Ohio, one of Trumps most ardent acolytes, delivered an impassioned speech, in which he portrayed the aid to Ukraine as the latest in a long series of catastrophic missteps by the internationalist forces in both parties that included the wars in Vietnam, Afghanistan, and Iraq.

Soon after the bill passed, first-term Republican Senator Eric Schmitt of Missouri noted a stark generational contrast in the vote. Nearly every Republican Senator under the age of 55 voted NO on this America Last bill, Schmitt posted on social media. 15 out of 17 elected since 2018 voted NO[.] Things are changing just not fast enough.

Just as revealing of the changing current in the party was the vote against the package by two GOP senators considered pillars of the partys internationalist wing: Lindsey Graham of South Carolina and Marco Rubio of Florida. Both also unequivocally defended Trump against criticism over his remarks at the South Carolina rally that seemed to encourage Putin to attack NATO countries that have not met the alliances guidelines for spending on their own defense.

To many observers, the retreat on Ukraine from Rubio and Graham suggests that even many GOP officials who dont share Trumps neo-isolationist views have concluded that they must accommodate his perspective to survive in a party firmly under his thumb. Lindsey Graham is a poster child for the hold that Donald Trump has over the Republican Party, Wendy Sherman, the former deputy secretary of state under President Joe Biden, told me.

Republican elected officials still demonstrate flickers of resistance to Trumps vision. In December, the Senate and the Republican-controlled House quietly included in the massive defense-authorization legislation a provision requiring any president to obtain congressional approval before withdrawing from NATO. The problem with that legislation is that a reelected Trump can undermine NATO without formally leaving it, said Daalder, who served as the U.S. ambassador to NATO under President Barack Obama.

You destroy NATO not by walking out but by just not doing anything, Daalder told me. If you go around saying If you get attacked, well send [only] a mine sweeper, Congress cant do anything. Congress can declare war, but it cant force the commander in chief to go to war.

Nikki Haley, Trumps former UN ambassador and his last remaining rival for the 2024 GOP presidential nomination, has stoutly defended the traditional Reaganite view that America must provide global leadership to resist authoritarianism. She has denounced Trumps comments on NATO, and she criticized him Friday for his repeated remarks over the years praising Putin following the reports that Alexei Navalny, the Russian leaders chief domestic opponent, had died in prison. On Saturday, in a social-media post, she blamed Putin for Navalnys death and pointedly challenged Trump to say whether he agreed.

Yet Haley has struggled to attract more than about one-third of the GOP electorate against Trump. Her foreign-policy agenda isnt the principal reason for that ceiling. But Trumps dominance in the race is evidence that, for most GOP voters, his praise for Putin and hostility to NATO are not disqualifying.

The new Chicago Council study helps explain why. Just since 2017, the share of Republicans most favorable toward Trump who say the U.S. should play an active role in global affairs has fallen inthe councils polling from about 70 percent to 40 percent. Likewise, only 40 percent of Trump Republicans support continued military aid to Ukraine, the study found. Only about that many of the Trump Republicans, the Council found, would support sending U.S. troops to fulfill the NATO treaty obligation to defend the Baltic countries if they were invaded by Russia.

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By contrast, among the part of the GOP less favorable to Trump, majorities still support an active U.S. role in global affairs, sending troops to the Baltics if Russia invades, and continued military and economic aid to Ukraine. The less-Trump side of the GOP was also much less likely to agree that the U.S. should reduce its commitment to NATO or withdraw entirely.

Conversely, Trump Republicans were much more likely to say that they want the United States to be the dominant world leader, while two-thirds of the non-Trump Republicans wanted the U.S. to share leadership with other countries, the traditional internationalist view.

Rather than the Biden administrations heavily alliance-focused approach to U.S. foreign policy, the report concludes, Trump Republicans seem to prefer a United States role that is more independent, less cooperative, and more inclined to use military force to deal with the threats they see as the most pressing, such as China, Iran, and migration across the United States-Mexico border.

The Chicago Council study found that the most significant demographic difference between these two groups was that the portion of the GOP more supportive of robust U.S. engagement with the world was much more likely to hold a four-year college degree. That suggests these foreign-policy concerns could join cultural disputes such as abortion and book bans as some of the issues Democrats use to try to pry away ordinarily Republican-leaning white-collar voters from Trump if hes the GOP nominee.

Jeremy Rosner, a Democratic political consultant who worked on public outreach for the National Security Council under Bill Clinton, told me its highly unlikely that Trumps specific views on NATO or maintaining the U.S. alliances with Japan or South Korea will become a decisive issue for many voters. More likely, Rosner said, is that Trumps growingly militant language about NATO and other foreign-policy issues will reinforce voter concerns that a second Trump term would trigger too much chaos and disorder on many fronts.

People dont like crazy in foreign policy, and theres a point at which the willingness to stand up to conventional wisdom or international pressure crosses the line from charmingly bold to frighteningly wacko, Rosner told me. To the extent hes espousing things in the international realm that are way over the line, it will add to that mosaic picture [among voters] that hes beyond the pale.

Perhaps aware of that risk, many Republican elected officials supporting Trump have gone to great lengths to downplay the implications of his remarks criticizing NATO or praising Putin and Chinas Xi Jinping. Rubio, for instance, insisted last week that he had zero concern that Trump would try to withdraw from NATO, because he did not do so as president.

Those assurances contrast with the repeated warnings from former national-security officials in both parties that Trump, having worn down the resistance in his party, is likely to do exactly what he says if reelected, at great risk to global stability. He doesnt understand the importance of the [NATO] alliance and how its critical to our security as well, Trumps former Defense Secretary Mark Esper said on CNN last week. I think its realistic that [if] he gets back in office, one of the first things hell do is cut off assistance to Ukraine if it isnt already cut off, and then begin trying to withdraw troops and ultimately withdraw from NATO.

A return to power for Trump would likely end the dominance of the internationalist wing that has held the upper hand in the GOP since Dwight Eisenhower. The bigger question is whether a second Trump term would also mean the effective end for the American-led system of alliances and international institutions that has underpinned the global order since World War II.