Senate Republicans are skeptical of Donald Trump’s aggressive new tariff plans — especially lawmakers from states with large agriculture industries that could bear the brunt of likely foreign retaliation.

“Tariffs have a place, but there is also the other side, which is: what about the repercussions of [countries] putting tariffs in a retaliatory method on some of our items as well?” added Sen. Mike Rounds (R-S.D.). “There is a place for tariffs, but I want to look at them case-by-case.”

Those sentiments were echoed by a number of Midwestern Republican senators this week as they returned from the election recess. And they hint at what’s likely to be a major source of tension within the party during the next Trump administration — over just how far the president should go in imposing tariffs, and whether he should work through Congress to do so.

Trump has proposed imposing up to a 20 percent tariff on all goods entering the U.S. and a 60 percent tariff on all imports from China. He also has much of the legal authority required to make good on his plans. But countries targeted by Trump’s broad tariffs, such as China and Mexico, are also the biggest buyers of U.S. farm goods and will likely strike back by cutting off business with U.S. farmers.

“I’m not for just arbitrary, across-the-board tariffs, but I think they’re a very, very useful tool in getting countries’ attention to play fair,” said Sen. John Boozman (R-Ark.), the top Republican on the Senate Agriculture Committee, who’s poised to become the chair next year.

South Dakota, the home state of Senate Republicans’ next leader, John Thune, relies on agriculture as its top economic driver, much of it led by exports of corn, soybeans and wheat.

Thune, a member of the Agriculture Committee and the Finance Committee, which is in charge of trade matters, has defended those interests during his four terms in the Senate. He’s also recently expressed reservations about tariffs, including an event with POLITICO at the Republican National Convention in July.

“I’m not a big fan of tariffs, and I made that clear during the last Trump administration for the reason you just mentioned, because the retaliatory action taken by countries with whom we need to do business and who are big markets for American agriculture,” Thune said, adding that an across-the-board tariff will require “some serious conversations.”

But given Trump’s resounding margins in the election, and the mandate he now claims, the politics are dicier for pro-trade Republicans. For now, many lawmakers are proceeding with caution.

“There’s pros and cons on tariffs. Obviously … a lot of people don’t really understand [that] tariffs sometimes are paid by the person that is importing, not the one that is exporting into your country,” said Sen. Tommy Tuberville (R-Ala.) — acknowledging a reality that Trump continues to deny. “So we got to be careful about that.”