Just days after the president announced in a haphazard manner that his administration would be imposing new tariffs on steel and aluminum, Republican lawmakers came out in droves to warn about the negative consequences they foresaw.

Their message on Monday was clear: The tariffs not only wouldn’t work, but they’d further endanger the party’s already shaky grip on its congressional majorities.

“The problem is bigger than the politics of one party or another’s messaging. The reality is tariffs are insanely stupid. And nobody ever wins a trade war. Both sides lose trade wars,” Sen. Ben Sasse (R-NE) told The Daily Beast. “Of course I want the Republican message to be effective in the midterm elections. But far more than that, we should all care about America’s economic growth.”

It was, perhaps, the most profound policy break within the Republican party since Trump took office. And it threatened to trample much of the goodwill that the president has built up within the ranks. GOP lawmakers fretted that in pushing for punitive, broad-based tariffs, Trump would not only wipe out the benefits of the tax-cut package that he and others had been touting since its passage late last year, but he would also overshadow the party’s positive economic message heading into this year’s midterm elections.

Voters, the worry went, would reap the benefits of a tax cut in their paycheck, but they would surely notice the uptick in the price of consumer goods they purchase daily.

“If the American consumer and what they have saved from our tax plan—if that dissipates due to the higher prices they would have to pay for goods based on some of these tariffs because the corporation is not going to absorb these costs… it is a concern,” said Rep. Mark Walker (R-NC), the chairman of the Republican Study Committee.

In public, an effort began in haste on Monday to persuade Trump to reverse course. AshLee Strong, a spokeswoman for House Speaker Paul Ryan (R-WI), told reporters the speaker was concerned that a trade war—even the threat of one—would “jeopardize” the economic growth since the tax legislation was signed into law. On Twitter, Ryan touted a meeting on Monday with European ambassadors “to discuss economic cooperation.”

Privately, the campaign to turn back Trump’s policy before it started was even more aggressive. Politico reported that top economic adviser Gary Cohn was set to bring in top officials from industries that would be hurt by the tariffs to allow them to make their case directly to Trump. A source familiar with discussions, meanwhile, told The Daily Beast that Ryan talked directly with Trump since the Thursday announcement on tariffs to make his case against them. The source also said that frustration was mounting among congressional Republicans over how the issue was handled, with their main liaison to the White House—the Office of Legislative Affairs—appearing to have been left in the dark, and with Trump’s adviser, Peter Navarro, seemingly given carte blanche to craft the policy.

“Navarro is not Senate confirmed—he’s in a position that has no statutory authority or accountability,” the source said. “He wants to slap tariffs on everything and start a trade war with our allies.”

The White House did not immediately return a request for comment.

On Capitol Hill, Republicans said they felt like they were re-litigating old debates over tariffs, including those passed in 2002—which, according to many independent studies, resulted in higher prices for consumers and job losses in the steel industry.

“You start increasing the prices worldwide of things like sheet aluminum and steel, that has a negative impact by raising the costs on people who utilize those products,” Sen. Ron Johnson (R-WI) told The Daily Beast. “In Wisconsin, there are a lot of manufacturers that utilize steel and aluminum, automakers and everything else, so it’s kind of hard to predict what kind of destruction that will cause in supply chains and, basically, GDP. How is that going to disrupt our own exports? It’s a risky move.”

In addition to their disagreements over the merits and concerns over the politics, Republican lawmakers also lamented how the administration handled the rollout of the new policy. The GOP chairmen of the Senate finance and commerce committees said they were not informed about the impending policy change in advance. “There is no standard operating practice with this administration,” Sen. John Thune (R-SD), who heads up the commerce committee, said bluntly. “Every day is a new adventure for us.”

Trump is notably prone to vacillate between policy positions. So it’s not inconceivable that private and public pressure for him to reverse course could work. But he has backed using the cudgel of tariffs since long before he ran for president. And those close to him say that he is as close to a true believer on this topic as he is on any.

Should he stay the course, there is little Congress could do to force his hand. And it’s not likely that lawmakers will take any action on an item that has historically been under the executive branch’s purview, even if they have a veto-proof majority.

“Trade votes are tough here,” Sen. Jeff Flake (R-AZ) told The Daily Beast. “Any trade deal before Congress will get politicized. It’ll be a shirts vs. skins kind of exercise. So this notion that we could exit out and somehow get a better deal is just crazy.”

They may have to live with it—electoral consequences and all. Flake, who has been critical of Trump on a number of fronts, said the new tariffs, if implemented, could make it harder for his counterparts to drive home a positive economic argument on the heels of the tax-code overhaul and the soaring stock market.

“We have a conducive tax and regulatory environment now, and the Trump administration has been good on that,” Flake told The Daily Beast. “But you can completely reverse that with bad trade policy.”