The counterpunches threaten to harm farmers in areas that supported Trump, such as Nebraska, Iowa and parts of Illinois. The actions by the Republican president put GOP lawmakers in a difficult spot as they fight off Democratic efforts to win congressional majorities in the midterm elections.

The escalation in tariffs proposed by the world's two largest economies could affect the GOP's ability to hold on to its congressional majorities in November.

Senators from states reliant on farming are pushing the president not to implement his proposed levies, which are designed to punish alleged unfair trade practices by China.

"He's threatening to light American agriculture on fire," Sen. Ben Sasse, R-Neb., said in a statement Thursday night. "Let's absolutely take on Chinese bad behavior, but with a plan that punishes them instead of us. This is the dumbest possible way to do this."

On Wednesday, as China proposed its retaliatory measures, Sasse's Republican Senate counterpart in Nebraska, as well as both of Iowa's GOP senators, urged Trump to reconsider the moves. Sen. Chuck Grassley of Iowa, a noted Trump ally, said, "Farmers and ranchers shouldn't be expected to bear the brunt of retaliation for the entire country."

Sen. Deb Fischer, who faces what should be an easy re-election bid this year in Nebraska, said Wednesday that she told the White House her state's farmers would face a "significant market loss" if China went through with its tariffs.



Trump has said recently in regard to the tariffs that a bit of temporary pain is worth it in the end.

Public opinion of the president's proposed tariffs is unclear at this point. It is not certain that views on Trump and GOP candidates in agricultural states will change significantly because of the proposals.

Still, the president's plans at least create a delicate situation for some Midwestern House Republicans already locked in tough fights for re-election.

One analyst of political risk for markets, Greg Valliere of Horizon Investments, told CNBC that a GOP source tells him the party is worried about political damage in states like Iowa. The Koch brothers' political network, a key financial source for Republican candidates and their agenda in the Midwest, has expressed frustrations with Trump's pursuit of tariffs, according to The Washington Post.

House Republicans facing tough re-election bids in states or districts with a major farming presence include Rep. Rod Blum of Iowa, Rep. Don Bacon of Nebraska and Rep. Mike Bost of Illinois. Nonpartisan election handicappers consider those races toss-ups and potentially crucial to whether Democrats flip the 24 GOP-held seats needed to take a House majority.

"I encourage the Administration to sit down and find a solution to this tariff war with China that protects the U.S.'s agricultural economy, promotes fair and free trade, and protects our intellectual property," Bacon said Friday in a statement. "It is time the president keeps his commitment to press for trade agreements with other countries that will expand our opportunities."

The offices of Blum and Bost did not give CNBC an immediate response to the tariff escalations with China. The House is out of Washington this week, so lawmakers could already be facing questions about the measures at home in their districts.

House Democrats' campaign arm has already started to criticize Bost and Rep. Rodney Davis, R-Ill., over the soybean tariffs. Davis' office did not immediately respond to CNBC's request on the congressman's tariff stance.

The tariffs also come as Republicans try to campaign on the tax overhaul passed in December, their signature achievement of Trump's first year in office. The fears about tariffs have sparked questions about whether the policy could overrule the GOP's economic messaging on taxes.

Trump's top economic advisor Larry Kudlow said Friday he is not worried about those repercussions.

"I will never let anything overshadow tax cuts," Kudlow said.

— CNBC's Patti Domm contributed to this report.