The Senate on Thursday passed a bipartisan resolution to curb President Trump’s ability to wage war against Iran in rare defiance of the White House and Senate Majority Leader Mitch McConnell.

Eight GOP senators joined all Democrats in a 55-45 vote to pass a war powers resolution that says Trump must win approval from Congress before engaging in further military action against Iran.

“It’s a rare day here in the Senate,” said Democratic Leader Sen. Chuck Schumer, fresh off the bitterly partisan impeachment fight. “I wish we didn’t have to say that, but it is. But the Senate just sent a clear shot across the bow: a bipartisan majority of senators don’t want the president waging war without congressional approval.”

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The measure now heads to the House. While it is expected to pass there, it's unlikely there's the two-thirds supermajority in both the House and Senate needed to override the expected Trump veto.

The eight Republicans who broke with Trump were Sens. Lamar Alexander of Tennessee, Lisa Murkowski of Alaska, Susan Collins of Maine, Mike Lee of Utah, Rand Paul of Kentucky, Jerry Moran of Kansas, Todd Young of Indiana and Bill Cassidy of Louisiana.

The measure was authored by Sen. Tim Kaine, D-Va., who said the resolution was not about Trump or even the presidency, but instead was an important reassertion of congressional power to declare war.

“After years of Congress avoiding its constitutional duty on matters of war, I’m grateful that a bipartisan majority of Senators affirmed that the president cannot send our troops into conflict without authorization,” Kaine said.

McConnell called the measure "deeply flawed" in a floor speech Wednesday. "It is too blunt and too broad," the Kentucky Republican said.

Trump argued in two tweets Wednesday that a vote against Kaine's proposal was important for national security and pointed to the Jan. 3 drone strike that killed Iran's top general, Qassem Soleimani.

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"We are doing very well with Iran and this is not the time to show weakness. Americans overwhelmingly support our attack on terrorist Soleimani," Trump said. "If my hands were tied, Iran would have a field day. Sends a very bad signal. The Democrats are only doing this as an attempt to embarrass the Republican Party. Don't let it happen!"

Tehran responded to the U.S. attack on Soleimani by launching missiles at two military bases in Iraq that house American and Coalition troops. The attack caused traumatic brain injuries in at least 64 U.S. soldiers, the Pentagon has said.

Democrats and Republicans alike criticized a briefing by the Trump administration shortly after the drone strike, saying U.S. officials offered vague information about a possible attack being planned by Iran but no substantial details.

Lee, who called it the "worst military briefing" he’s ever had, said Congress cannot escape its constitutional responsibility to act on matters of war and peace.

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"We want to make sure that any military action that needs to be authorized is in fact properly authorized by Congress," said Lee, noting he agrees with Trump's foreign policy. "That doesn't show weakness. That shows strength.”

The Associated Press and Fox News' Chad Pergram contributed to this report.