A day before President Trump struck a preliminary trade deal with the Europeans, Republican Sen. Mike Rounds of South Dakota privately delivered a somber message to his Republican colleagues.

On his trips home of late, he told senators at their private weekly lunch, he was seeing fewer of the red “Make America Great Again” hats, the once-ubiquitous display of support for Trump.

Rounds’s comment, confirmed by two senators in the room who spoke about the meeting on the condition of anonymity, reflected a rising fear among Republican officials that Trump’s trade war was dimming enthusiasm among the party faithful — and potentially undercutting the GOP effort to keep control of Congress in November.

Republican anxiety about whether Trump’s trade war will undo the GOP’s message on the strong economy reached a fever pitch this week, with numerous Republican lawmakers coming out with sharply worded attacks on the president’s trade strategy.

Those frustrations, which had been building for weeks, cooled somewhat Wednesday afternoon after Trump and European Commission President Jean-Claude Juncker agreed to take steps to resolve the trade conflict between the European Union and the United States.

Trump and Juncker announced that the E.U. would buy more soybeans and, eventually, liquefied natural gas from the United States in exchange for a U.S. reexamination of measures including tariffs on aluminum and steel.

The White House did not say whether Trump acted in a conciliatory fashion because of the Republican opposition to his trade strategy. But the president made a point of welcoming lawmakers, who were at the White House to press him on trade, to the Rose Garden ceremony with Juncker.

Rounds called the deal “a step in the right direction.”

“We understand that they’re working on a number of other smaller [trade deals]. And, hopefully, those will start to come to fruition,” Rounds said. “That will make people in my part of the country a lot more comfortable with the negotiations.”

Sen. Joni Ernst (R-Iowa), who had previously warned of “fallout” from Trump’s approach to trade, praised the president in a tweet.

“Soybeans are a big deal in #Iowa. Thank you @realDonaldTrump for engaging the European Union and working toward a win for U.S. #farmers,” she wrote.

It is not clear whether the respite from Trump’s trade conflict will prove sustainable or how significant it ultimately will be. Trump on multiple occasions has taken steps to defuse tensions, only to resume hostilities shortly after. Any final deal must be seen as acceptable to a range of leaders in Europe, any one of whom could issue a statement that offends Trump and upends the entire process.

And the deal with the E.U. does not end the trade conflict with China, which is targeting U.S. farm states, where farmers have seen prices fall and orders shrink as trading partners impose tariffs on U.S. agricultural products. Soybean farmers have been especially targeted.

Rep. Dan Newhouse (R-Wash.), who attended the trade meeting at the White House on Wednesday, said he thanked Trump for taking on the trade issue but informed him that China is the No. 1 customer for Washington state’s cherries.

“It’s really impacted our markets,” Newhouse said of China’s retaliatory tariffs. “I expressed to him our farmers are with you, but they’re also feeling the impact of these tariffs. And that’s when we talked about the importance of getting this done as soon as possible. And he understands that.”

“There’s a lot of angst in farm country,” Newhouse added. But he said the deal with the E.U. gave him more confidence in Trump’s approach.

Before the announcement of the limited trade deal, Republicans had sounded growing alarm that the trade battle would weigh on their electoral prospects.

“I think that the midterms are going to be determined by whether they see economic growth, economic opportunity, and I believe in the midterms they’ll continue to see that,” Sen. Cory Gardner (R-Colo.), who chairs the Senate GOP campaign committee, said earlier Wednesday.

But Gardner added: “I certainly think that tariffs create a risk to the economy.”

On Tuesday, the Trump administration unveiled a plan to begin distributing as much as $12 billion in emergency aid to farmers in September. The plan was broadly panned by GOP officials, who called on Trump to de-escalate the trade disputes rather than blunt the pain they are inflicting on farmers.

In Ohio on Wednesday as he opened the state fair, Gov. John Kasich (R), a former presidential primary opponent of Trump’s, slammed the bailout and questioned the motivation for it.

“You have to wonder: Is this about vote-buying?” Kasich said. “Is this about the fact that you don’t want farmers turning against you in a midterm when they are suffering the consequences of trade?”

Forty-nine percent of voters said they thought raising tariffs and barriers to imports would do more to raise the cost of goods and hurt the economy, according to an NBC News/Wall Street Journal poll conducted this month. Just 25 percent said they believed the tariffs and barriers would help the economy.

Chris Wilson, a Republican pollster who is working on several Senate races, said it was too early to predict any fallout from Trump’s trade war because there is still time for the president’s bet to pay off, which would be a win for free trade and for the United States.

“If it’s a win, it will be a major issue for the GOP,” Wilson said in an email. “However, if other countries don’t negotiate down trade barriers; if they assume Trump is going to back down — against all evidence — then we’re looking at the possibility of a global recession. Clearly, that would be a major issue for Democrats.”

In the battle for the Senate, Republican officials are particularly worried about the impact of the tariffs in Tennessee, Florida, Missouri and North Dakota — all states featuring marquee contests that could decide the Senate majority.

From whiskey and automobiles produced in Tennessee to oranges in Florida, Republicans are nervous that homegrown products caught in the middle of a trade war could make it harder for Republican candidates to be competitive in November.

In North Dakota, Sen. Heidi Heitkamp (D) has repeatedly underscored her concerns about the effects of Trump’s trade agenda on her largely agricultural state. In Tennessee, former governor Phil Bredesen, the likely Democratic nominee for the U.S. Senate, has run an ad criticizing the tariffs.

The E.U. trade deal, if it holds, could provide relief to Republicans in states such as Tennessee and South Carolina that are home to major foreign auto manufacturers. Trump has been pursuing tariffs on foreign automakers, but those plans seemed on hold Wednesday after the E.U. agreement.

On Wednesday, Sen. Lamar Alexander (R-Tenn.) had introduced legislation along with Sen. Doug Jones (D-Ala.) that would inhibit Trump’s ability to impose the auto import tariffs.

“Shooting yourself in both feet at once is not the right solution to our problem — which is what will happen if we continue these tariffs,” Alexander said.

Damian Paletta contributed to this report.