Pompeo “didn’t show us any evidence” about his reasons Washington is so concerned about potential Iranian aggression, said one senior European official who took part in one of Pompeo’s meetings. The official’s delegation left the meeting unconvinced of the American case and puzzled about why Pompeo had come at all.

Many officials in European capitals said they fear that conflict with Iran could have a cascading effect on their relations with Washington, ripping open divisions on unrelated issues.

They distrust Trump’s Iran policy, fearing that key White House advisers are ginning up rationales for war. And leaders need to win reelection from citizens who hold Trump in low regard and would punish them for fighting alongside Americans on the Iran issue.

Democratic members of Congress, while traditionally strong supporters of pressuring Iran, have also raised questions about the intelligence and the administration’s apparent flirtation with combat. In a statement on the Senate floor on Wednesday, Sen. Robert Menendez (N.J.), the ranking Democrat on the Senate Foreign Relations Committee, demanded “answers from this administration about Iran . . . and about what intelligence this administration has.” So far, he said, the administration has ignored those demands and refused to provide briefings.

“We cannot, and we will not, be led into dangerous military adventurism,” he said.

Anxieties over the heightened threat environment spilled over into Capitol Hill on Wednesday during a classified briefing. Rep. Liz Cheney (R-Wyo.) argued that the intelligence warranted an escalation against Iran, said one person with knowledge of the briefing. In response, Democratic Rep. Seth Moulton (Mass.) accused her of exaggerating the threat in what the person described as a “very heated exchange.”

A representative for Moulton declined to comment. A spokesman for Cheney said the congresswoman “will never comment on classified briefings and believes that any member or staffer who does puts the security of the nation at risk.”

Michael Birnbaum in Brussels, Simon Denyer in Tokyo and Missy Ryan, Karen DeYoung and Carol Morello in Washington contributed to this report.