Efforts in Congress to limit President Trump’s ability to launch a preemptive strike against Iran are gaining steam, with more than a dozen House members and leading Senate Democrats saying they want to reassert the Article I branch’s power. The president has said he is trying to restart negotiations with the Islamic Republic before making a decision about targeted strikes. 

Mr. Trump has faced intense criticism from the left and right as he weighs his options with respect to Iran. Influential commentators like Tucker Carlson and Steve Bannon have said the president must stay out of the war. Mr. Trump, meanwhile, says he will make his decision within the next two weeks based on the state of negotiations with Iran about its nuclear program. 

A resolution introduced by a Republican congressman, Thomas Massie, and a Democratic congressman, Ro Khanna, has already garnered 17 supporters in the House. That measure would require the president to come to Congress if he wants to strike Iran, unless the United States is imminently threatened. 

Mr. Massie is the only GOP signatory, and the Democrats backing the measure mostly come from the Progressive Caucus. 

“The United States is not at war with Iran. Any offensive military action taken by the U.S. must receive a vote in Congress,” Congresswoman Betty McCollum, a liberal lawmaker of Minnesota, said. 

Congresswoman Marjorie Taylor Greene has told Mr. Trump that he needs to stay out of this conflict, though she has stopped short of signing on to the Massie–Khanna resolution. 

“While I’m opposed to [U.S.] involvement in foreign wars and regime change, I do not see a need to sign on to Rep. Massie’s war powers resolution yet as we are not attacking Iran,” Ms. Greene told Fox News. 

Senator Kaine has introduced a similar resolution in the Senate, which is expected to receive a vote in the upper chamber by the end of next week. He says that there are multiple Republican members who have told him privately that they will likely back the resolution. 

“I’ve had some who tell me they’re likely to support it. They’re making their own decisions about when they announce that or when they sign on,” Mr. Kaine told the Sun earlier this week. 

Senate Democratic leadership hinted on Tuesday that it was important for Congress to take some role in having oversight of Mr. Trump’s military aims and plans. 

“By law, the president must consult Congress and seek authorization if he is considering taking the country to war,” Senator Schumer wrote in a joint statement with other top Democratic senators. “He owes Congress and the American people a strategy for U.S. engagement in the region.”

“We need a clear, detailed plan outlining the goals, risks, cost, and timeline for any proposed mission, as well as how he will ensure the safe evacuation of Americans in harm’s way all across the region,” the senators write. “We demand immediate, detailed answers on these and other urgent matters to determine the way forward.”

Senator Sanders said definitively Wednesday that Congress needs not only to reassert its roles in military affairs, but that the Israel–Iran War is the making of Prime Minister Netanyahu. 

“Netanyahu was wrong regarding the war in Iraq. He is wrong now. We must not get involved in Netanyahu’s war against Iran,” Mr. Sanders said in a statement.