WASHINGTON — Over the past week, congressional Republicans have gotten a glimpse of the President Trump they hoped to never see.
On gun safety and, more significantly to many of them, trade, the president has loudly broken with longstanding party orthodoxy and reminded Republican leaders on Capitol Hill that they can never be 100 percent certain of what they are going to get with the onetime New York Democrat.
Despite such worries, Mr. Trump’s first-year actions on policy and personnel — particularly judicial nominees — provided substantial reassurance to congressional Republicans. They concluded that Mr. Trump was really one of them when it came to bedrock issues and that the anti-Washington, drain-the-swamp cries from the raucous campaign rallies were only so many applause lines.
In the chaos of the early weeks of his administration, Mr. Trump provoked a sigh of relief from Senator Mitch McConnell, Republican of Kentucky and the majority leader, that the president seemed to actually be conservative. “If you look at the steps that have been taken so far, looks good to me,” Mr. McConnell said.
Now here comes Mr. Trump with his sudden proposal to rebuild the country’s steel and aluminum industries through steep tariffs on imports from leading trading partners. Most congressional Republicans fundamentally disagree with that approach, which they consider a backdoor tax that could easily touch off a calamitous trade war, hurt their local businesses and overwhelm any gains from their hard-won, Republican-only tax bill.
Already facing a harsh political climate heading toward the November midterm elections, Republicans fear that moving ahead with the tariffs could send the party — not to mention the economy — spiraling in the wrong direction. Republicans are banking on a robust economy that they can attribute to their tax cuts and regulatory rollbacks to overcome the deep public disapproval of Mr. Trump exhibited in multiple elections last year. They don’t want to do anything that could threaten economic gains.
“The economy is moving in the right direction; that is what we are working on,” Senator John Thune of South Dakota, the chamber’s No. 3 Republican, told reporters on Tuesday. “We are going to stay focused on a pro-growth, pro-jobs agenda.”
Mr. McConnell had remained quiet about the tariffs since Mr. Trump unexpectedly announced them last week. But on Tuesday, he made it very clear that he, and almost all of his colleagues, have major problems with them.
“There’s a high level of concern about interfering with what appears to be an economy that’s taking off in every respect,” Mr. McConnell said. “I think the best way to characterize where I am, and where our members are, is we are urging caution that this develop into something much more dramatic that could send the economy in the wrong direction.”
This major policy divide goes to a disconnect between the president and congressional Republican leaders that has been papered over by fights with Democrats over the past year as well as the party unity behind the tax bill.
Most of the Republican leaders on Capitol Hill remain firmly aligned with big business and want to retain the strong support of advocacy groups such as the U.S. Chamber of Commerce and organizations affiliated with David H. and Charles G. Koch. Those business factions, always important to Republicans in a campaign year, do not like new tariffs.
Mr. Trump, on the other hand, has for years preached about the dangers and disadvantages of free trade and the harm it has done to once-leading American industries. Republicans now hoping to talk the president down from his tariff stance may find that his campaign promises about protectionism are ones he truly wants to keep.
It is a similar situation with gun safety. Mr. Trump has in the past backed the idea of an assault weapons ban. But congressional Republicans figured that his strong campaign embrace of the National Rifle Association would keep him securely in the anti-gun-control corner.
Then, in last week’s extraordinary public White House meeting after the Parkland, Fla., school massacre, Mr. Trump embraced multiple aspects of the gun control agenda. He even uttered the words “take the guns first” — a phrase previously unthinkable for a top Republican politician given the party’s history on gun rights.
Republicans were aghast. They also figured that, under pressure from his allies at the N.R.A., Mr. Trump would quickly return to the fold and let his enthusiasm for gun control wane. More important, congressional Republicans also knew that gun control legislation was really in their hands, not the administration’s, and that they could easily bottle up any proposal.
But tariffs are a completely different matter, with the president given wide latitude to act on international trade policy. Republicans, who say they have little legislative recourse, are now engaged in a furious effort to pull the president back from making too sweeping a decision.
They are also treading carefully to avoid antagonizing a mercurial figure whose mind they still hope to change as they have in previous cases where he drifted from the party line, such as on immigration.
Speaker Paul D. Ryan, for instance, was careful to credit Mr. Trump on Tuesday for exposing that some countries do take advantage of the trade rules.
“The president’s right to point out that there are abuses,” Mr. Ryan said. “There clearly is dumping and transshipping of steel and aluminum.”
Referring to any trade restrictions, Mr. Ryan said that Republicans simply “want to make sure that it’s done in a prudent way that’s more surgical, so we can limit unintended consequences.”
As for Mr. McConnell, he said that “we need to wait and see what the White House finally decides to do on this.”
Mr. McConnell would no doubt prefer that Mr. Trump revert to the conventional conservative principles the senator found so comforting last year. But this break could prove to be real, putting Mr. Trump and his Republican allies at cross-purposes at an inauspicious moment on the political calendar.