President Trump says he will pull more U.S. troops from Germany after an initial reduction of 5,000, while Republican leaders in Congress say they’re “very concerned” about the move and the signal it sends to America’s adversaries.

The fast-moving developments surrounding America’s force posture in Europe are directly tied to the U.S.-Iran war. Late last week, the Pentagon said it would pull about 5,000 troops from Germany in the midst of a public clash between Mr. Trump and German Chancellor Friedrich Merz over the U.S. strategy in the Iran conflict.

About 35,000 U.S. active-duty military personnel are based in Germany, representing the largest U.S. troop presence in Europe. The Pentagon said the reduction of 5,000 will be completed within 12 months.

Mr. Trump said he’s prepared to go much further.

“We’re going to cut way down. And we’re cutting a lot further than 5,000,” the president told reporters in Florida on Saturday.

Key Republicans expressed concern about the decision. They pointed to Germany’s significantly increased defense spending, something Mr. Trump has long pushed European allies to do.

In a joint statement Saturday, Mississippi Sen. Roger Wicker and Alabama Rep. Mike Rogers — the Republican chairmen of the Senate and House Armed Services committees, respectively — pressed the Pentagon to keep those troops in Europe and to explain the rationale behind the move to Congress.

“We are very concerned by the decision to withdraw a U.S. brigade from Germany. Germany has stepped up in response to President Trump’s call for greater burden sharing, significantly increasing defense spending and providing seamless access, basing, and overflight for U.S. forces in support of Operation Epic Fury,” the senators said, referring to the U.S. operation against Iran.

“The reality remains even as allies move toward spending 5% of GDP on defense, translating that investment into the military capability needed to assume primary responsibility for conventional deterrence will take time,” they said. “Prematurely reducing America’s forward presence in Europe before those capabilities are fully realized risks undermining deterrence and sending the wrong signal to [Russian President] Vladimir Putin.”

Last week, Mr. Merz was especially pointed in his criticism of the U.S. approach in Iran.

“The Americans clearly have no strategy, and the problem with conflicts like this is always that you don’t just have to go in; you also have to get out again,” the German chancellor said on April 28.

Just three days later, the Pentagon announced the drawdown of 5,000 troops from Germany.

NATO officials said they want more information about the strategy behind the move. They also said it demonstrates that European nations must take greater responsibility for their own defense, rather than relying on the U.S.

“We are working with the U.S. to understand the details of their decision on force posture in Germany,” NATO spokesperson Allison Hart posted on social media. “This adjustment underscores the need for Europe to continue to invest more in defence and take on a greater share of the responsibility for our shared security” on the continent.