WASHINGTON — Congressional Republicans are maneuvering to stop President Donald Trump from levying harsh tariffs on steel and aluminum imports, arguing that the move runs counter to the core of their economic agenda and could even cause political problems heading into the 2018 midterms.

“We are extremely worried about the consequences of a trade war and are urging the White House to not advance with this plan,” AshLee Strong, a spokeswoman for House Speaker Paul Ryan, R-Wis., said in a statement Monday. “The new tax reform law has boosted the economy and we certainly don’t want to jeopardize those gains.”

Members of the House Ways and Means Committee were also circulating a letter criticizing the tariffs, while high-ranking Senate Republicans voiced their own opposition. “My constituents are worried about the cost of their beer cans. It’s a concern,” said Sen. John Cornyn, R-Texas. “The price of cars. A tariff obviously is going to get passed on to the consumer eventually in the price of goods and that ought to be everybody’s concern.”

Amid mounting Republican dismay over Trump’s protectionist path, Sen. Orrin Hatch, R-Utah, chairman of the Senate Finance Committee, predicted the president ultimately will back off plans for the new trade levies.

“I think he’s thinking it through. We’ll see,” Hatch said Monday. “I think he’s shooting one across the bow and letting people know that we’re not being treated fairly in these international matters, and frankly I don’t blame him.

Hatch blamed White House trade adviser, Peter Navarro, for encouraging Trump to impose the tariffs. The veteran Republican said he had written the president to urge him to reverse his decision, adding: “I think it would be a tragedy if they continue on the course that was announced.”

It’s unclear whether the GOP pushback will have any effect on Trump, who surprised fellow Republicans on Thursday when he announced tariffs of 25 percent on steel and 10 percent on aluminum. He has repeatedly defended the plans, and after the statement from Ryan’s office Monday, the president said in Oval Office remarks that he was “not backing down.”

White House officials still have not decided how precisely the tariffs will be applied or how broadly they will be imposed, according to two people briefed on the discussions who were not authorized to speak publicly. There was still an active debate among top advisers to exempt Canada, Mexico and the United Kingdom, with supporters of this move alleging these countries don’t pose a national security risk. Trump has tried to use the threat of tariffs to force Mexico and Canada to capitulate on the NAFTA negotiations, and it remains unclear where Trump will ultimately land.

For all of the controversies Trump has faced, the tariffs decision marks one of the few times he has taken a step that runs directly counter to congressional Republicans’ legislative and economic goals. Many lawmakers have voiced concerns that the move will undermine the $1.5 trillion tax cut bill they passed in December.

They also said it could cause political problems ahead of this year’s midterm elections. Democrats hope to take back control of the House and Senate in November, while Republicans planned to run on an economic argument to defend their majorities.

But it is difficult to predict how far Republicans would go to stand up to Trump, who remains popular with core GOP voters.

The tariff decision has not been finalized, but that is expected to happen later this week or next. Congressional Republicans want to prevent that from happening — but are considering fallback options, according to a congressional aide who spoke anonymously to discuss the private deliberations.

The Constitution gives Congress authority over taxation and tariffs.

A spokeswoman for House Ways and Means Committee Chairman Kevin Brady, R-Texas, said in a statement that “the administration and Congress must work together on trade policies that build off the momentum of the president’s tax cuts, which is why any tariffs should be narrow, targeted, and focused on addressing unfairly traded products, without disrupting the flow of fairly traded products for American businesses and consumers.”

Trump dismissed fears Monday that the trade moves could damage the economy.

“Our country on trade has been ripped off by virtually every country in the world, whether it’s friend or anybody — China, Russia, people we think are wonderful, the European Union,” Trump said while meeting with Israeli Prime Minister Benjamin Netanyahu in the Oval Office. “We lost $800 billion a year on trade. Not going to happen.”

Republicans and others have warned that major U.S. trading partners could retaliate by imposing tariffs on U.S. products, but Trump, who tweeted Friday that a trade war would be “easy to win,” dismissed those concerns as well.