President Trump pauses as he speaks onstage during a rally in Great Falls, Mont., on July 5. (Tim Goessman/Bloomberg News)

President Trump’s transformation of the Republican Party is taking full root — with the president in recent days shunning traditional alliances and values that have long been core tenets of the GOP.

The leader of what was once the party of free and open commerce escalated a trade war with China this month as the world’s two largest economies put in place new tariffs. Trump signaled that he plans to take a combative approach to the upcoming NATO summit, questioning the value of the alliance and warning Germany during a raucous political rally in Montana last week that “I don't know how much protection we get by protecting you.”

Even his signature hard-line immigration rhetoric is increasingly inflammatory — Trump accused Democrats last week of wanting “anarchy, amnesty and chaos” while insisting that migrants arriving at the border must be told “OUT . . . just as they would if they were standing on your front lawn.”

The hardening of Trump’s positions on key parts of his “America First” agenda comes just four months before November’s midterm elections. That is increasing the pressure on congressional Republicans to either embrace the most controversial tenets of his presidency or attempt to distance themselves from them in hopes of attracting the independent voters they are likely to need to retain control of Congress.

“I think that’s the drama we’re going to see in the next few years — whether the beliefs that are being espoused by President Trump are going to firmly take root and take over the party, or are they going to be tested in real life,” said Tony Fratto, who served as a spokesman in the George W. Bush administration. “I think we’re going to see foreign policy failures and trade failures that will lead Republicans to say, that was a mistake. We need to go back to where we were on those issues.”

But the president’s allies say Trump’s message of American dominance, even at the risk of retreating from traditional Republican principles, resonates deeply with voters who have long shared Trump’s skepticism of military alliances and trade deals. Polls show that Trump remains immensely popular within the Republican Party — indicating that, for now, efforts to confront Trumpism from within are likely to be a losing battle.

“They want to see America first,” said Sen. Steve Daines (R-Mont.), who represents one of the biggest Senate battlegrounds this fall and accompanied Trump to the rally in Great Falls last week. “They want to see jobs protected. And relating to NATO, they want to make sure everybody’s paying their fair share.”

The tensions among Republicans over Trump’s recent actions and comments come as the president takes the international stage this week, first at the annual NATO summit in Brussels, then Britain — where protests are expected to greet him, particularly in London — and finally next week in Helsinki, where Trump is to meet one-on-one with Russian President Vladi­mir Putin.

In advance of the stops abroad, Trump has taken a confrontational tone with allies, promising to tell NATO that “you got to start paying your bills” and complaining that European nations “kill us on trade.” 

“They make it impossible to do business in Europe, and yet they come in and they sell their Mercedes and their BMWs to us,” Trump said. “So we have $151 billion in trade deficits with the E.U. And on top of that, they kill us with NATO. They kill us.”

Trump also mocked critics of his closely watched summit with Putin and defended the former KGB agent: “You know what? Putin’s fine. He’s fine. We’re all fine. We’re people.”

GOP lawmakers endeavored to send a different message on their own trip to Russia and surrounding nations last week — a mission that sought to rebuild the frayed relationship with Moscow while stressing that Russia’s meddling in the 2016 U.S. presidential election was unacceptable. 

Before the Republicans traveled to Russia, they met with officials in Norway, a fellow NATO country. Sen. John Thune (R-S.D.), who was part of the delegation, said that while lawmakers stressed the importance of all countries making their contributions to NATO, they also wanted to make clear “from the congressional standpoint that we are very much committed to the alliance.”

“I hope that in the meetings with our NATO allies, that what comes out of that is a unified front,” Thune said of Trump’s upcoming European trip. “It makes it much harder for the Russians to make it an us versus them . . . issue if the Europeans and the NATO allies, we’re all on the same side.”

But indications are that Trump’s message out of the NATO summit will be far less accommodating. In addition to his comments at the Montana rally, Trump told senior aides recently that he wants to slash U.S. spending on Europe’s defense if allies are unwilling to contribute more to NATO, a senior administration official told The Washington Post. 

In tweets on Monday morning, Trump again voiced his objections to lower levels of spending by other NATO members, particularly Germany, saying the situation “is not fair, nor is it acceptable.”

In April, during a visit with French President Emmanuel Macron, Trump was sharply critical of both British Prime Minister Theresa May and German Chancellor Angela Merkel, U.S. and European officials said. Trump is scheduled to meet with May in London after the NATO summit, and Merkel has been a frequent target of Trump’s ire. 

Few principles of the Trump doctrine have rankled Republicans more than trade, with GOP lawmakers reticent to embrace the president’s protectionist tendencies while Trump stands firmly behind them. 

The impact of Trump’s tariffs came into much sharper view this past week. On July 1, Canada officially imposed billions of retaliatory measures on U.S. products — such as yogurt and whiskey — in response to Trump’s tariffs on Canadian steel and aluminum. 

On Friday, the U.S. slapped duties on $34 billion in Chinese goods, prompting accusations from China that the United States had violated World Trade Organization rules and making it even more likely that Beijing will follow through on a pledge to impose levies on U.S. agricultural goods.

While Trump travels throughout the continent next week, pressure is likely to build again on Capitol Hill for legislative action to rein in Trump’s tariffs as the global trade war deepens. Sens. Patrick J. Toomey (R-Pa.) and Bob Corker (R-Tenn.) are clamoring for a vote on their proposed legislation requiring congressional approval for tariffs imposed under a law intended to address national security concerns. 

They have yet to secure that vote, and some Republican lawmakers say their constituents continue to put faith in Trump’s negotiating tactics — even if the president’s tariff policies run counter to the party’s traditional free-trade values. 

“I think a lot of Republicans are cutting the president some slack and giving him an opportunity to try to deal with trade abuses with certain countries and giving him the maximum amount of leverage,” said Thune, who has been a vocal critic of the administration’s trade policies. 

But noting that he plans to meet with soybean farmers from South Dakota this week in Washington, Thune added, “Some of the stuff is starting to bite.”

“What I’m saying to constituents is, give President Trump some room,” said Rep. Steve King (R), whose northwestern Iowa district produces massive quantities of pork and soybeans — products among the most vulnerable to Chinese retaliation. “Give him some room to freely negotiate here, and let’s see how it comes out. Don’t undercut the president and take the leverage away.”