Collins on Tuesday said Congress can't be sidelined on important decisions.

"The Kaine resolution would continue to allow the President to respond to emergencies created by aggression from any hostile nation, including Iran, and to repel an imminent attack by Iran or its proxy forces," she said in a statement. "It simply makes clear that only the Legislative Branch may declare war or commit our armed forces to a sustained military conflict with Iran.”

Lee and Paul said last week they would also back Kaine's resolution after some changes to its language. Lee announced his support after top Trump administration officials briefed lawmakers about the killing of top Iranian general Qassem Soleimani, which the Utah Republican described as “the worst” he’d seen on a military issue in his nine years in the Senate.

Kaine filed a revised version of his resolution last week and could force a vote on it as soon as early next week, unless there’s a unanimous consent agreement. But the Senate impeachment trial could affect the vote’s timing.

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Senate Minority Leader Chuck Schumer said Tuesday the Senate still needs to work out the timing with impeachment but the "resolution is the right way to go and has the support of all 47 Democrats."

Kaine’s resolution limits the Trump administration’s military actions against Iran without congressional approval. The House passed a similar symbolic measure last week.

Burgess Everett contributed to this report.