Just a week removed from their acquittal of President Trump, U.S. senators—including a number of Republicans—are set to deliver the president a constitutional dressing-down over who has the power to authorize war with Iran.

On Thursday, a bipartisan majority of the GOP-controlled Senate is expected to vote in favor of a War Powers Act resolution that blocks the U.S. from engaging in hostilities with Iran without express approval from Congress. Similar resolutions have passed the Democratic-led House of Representatives since Jan. 3, when U.S. forces, at Trump’s direction, assassinated the Iranian general Qassem Soleimani.

The Senate has been slower to move, largely due  to the impeachment trial that froze the chamber for two weeks. In the time that has passed, the administration’s handling of Soleimani has faded from the headlines—but champions of the resolution, particularly Sen. Tim Kaine (D-VA), got time to tweak the resolution and win over GOP support. 

The success of those efforts became clear on Wednesday, when eight Republican senators voted with all Democrats to allow the War Powers resolution to proceed. The group included the GOP’s reliable dissenters on foreign policy, Sens. Rand Paul (R-KY) and Mike Lee (R-UT), as well as moderates like Sen. Susan Collins (R-ME) and one of the swing lawmakers who helped secure Trump’s speedy acquittal, Sen. Lamar Alexander (R-TN). 

A knowledgeable Senate Democratic aide said there’s high confidence that number will hold for the final vote on Thursday. "We'll be sending Trump his second War Powers resolution,” the aide told The Daily Beast. 

If that tally sticks, it would represent a greater GOP rebuke of Trump’s war authority than the first War Powers resolution, which moved to end U.S. support of the Saudi war in Yemen. Seven Republicans voted in favor of that resolution; Trump ultimately vetoed it when it passed in May 2019, and there weren’t enough votes to override it.

That’ll likely be the case again with the Iran resolution, but its lead backers argue that the vote will nevertheless send a strong message that the legislative branch won’t sit idly by as the executive bypasses Congress on a military move that significantly increases prospects for war with Iran. 

It could even deter Trump from similar moves in the future, said Kaine, who raised the example of last year’s Yemen resolution. “We couldn’t override it, but it changed his behavior and decision-making,” the Virginia Democrat said at a Wednesday press conference. “He didn't like Congress telling him what to do, but that our feeling is when Congress stands up and acts, a majority of both bodies, and puts something on his desk, even if he chooses to veto it and we can’t override… That is something that could well be a factor in his decision making .”

Trump, for his part, took to Twitter on Wednesday to urge the Senate to reject the resolution, claiming it would “show weakness” to America’s adversaries, particularly Iran, which he suggested would have a “field day” if it passed. Majority Leader Mitch McConnell (R-KY) has also voiced strong opposition to the resolution on similar grounds.

GOP backers of the resolution straddled a fine line between praising Trump’s action on Soleimani—recognizing the executive’s prerogative to respond to foreign attacks—and explaining why this resolution to rein in the president is necessary.

“This is not about the presidency,” said Lee, who said he is a “huge fan” of the way Trump has exercised his authority as commander in chief. “This is not about wanting a weak presidency, or a weak commander in chief… This is neither hawkish or dovish.” Instead, Lee said, the resolution focuses on the fact that “moving forward, any action that we take involving Iran… needs to be authorized by Congress.”

“This,” he said, “should not be controversial.” 

—with reporting from Spencer Ackerman