A handful of Republican senators joined their Democratic colleagues Thursday to pass a resolution calling on President Donald Trump to "terminate the use of U.S. Armed Forces for hostilities against Iran" unless those actions are authorized by Congress.
The U.S. Senate passed the bipartisan war powers resolution by a vote of 55-45.
Trump is expected to veto the measure, arguing it would be dangerous to limit his war-making power.
"It is very important for our Country's SECURITY that the United States Senate not vote for the Iran War Powers Resolution," Trump said on Twitter Wednesday. "We are doing very well with Iran and this is not the time to show weakness."
Trump said he had overwhelming American public support for the airstrike last month that killed Iranian general Qassem Soleimani.
"If my hands were tied, Iran would have a field day," he said. "Sends a very bad signal. The Democrats are only doing this as an attempt to embarrass the Republican Party. Don't let it happen!"
But Democratic Senator Tim Kaine, the resolution’s co-sponsor, argued it was time to reassert the U.S. Congress’ constitutional authority to declare war as tensions between the U.S. and Iran increased following the death of Soleimani.
"War is the most solemn responsibility we have," Kaine said of the Senate Thursday. "We have a special obligation to make sure that we deliberate and deliberate carefully before we send troops into harm's way. The president of the United States — this president and every president — always needs the ability to defend the United States against imminent attack without asking for anybody's permission. I think the world knows we will do that. This body, though, is the body that needs to decide if we go on offense and engage in military action."
Republican support for the measure comes a little over a week after members of the president's own party voted to acquit him of charges in the Senate impeachment trial.
But in floor remarks Thursday, Senate Majority Leader Chuck Schumer addressed criticism of the resolution, saying it was not an attempt to embarrass Trump.
"Well, then why are a good number of Republicans supporting it?" Schumer said. "This resolution is going to pass with a bipartisan majority of Senators in support — a rarity these days. If this is purely an attempt to embarrass the president, well, it’s going to be a bipartisan one."
But supporters of the resolution were unable to muster a two-thirds vote that would override an expected presidential veto.
Senate Republican Leader Mitch McConnell, asked in opposition to the measure Wednesday, "What message will the Senate send to American service members? Should they doubt whether their own leaders are authorized to defend them?"
He said, "What message should we send to our regional allies and partners? Can they count on continued solidarity from the United States? What would it say to a real great-power, competitors like Russia and China, if we cannot even remain united in the face of a lesser challenger such as Iran? Let's send the right message with our votes. Let's defeat this misguided resolution."
Another Republican lawmaker, Senator John Thune, said Trump's killing of Soleimani was justified, calling the war powers resolution "an ill-advised and potentially problematic response to the president's action."
The killing of Soleimani heightened tensions between the United States and Iran last month, reviving a long-running debate over the role Congress should play in overseeing the president's ability to manage foreign military operations.
In the nearly two decades since the Sept. 11, 2001, terrorist attacks, U.S. lawmakers have revisited the issue of congressional approval for conflicts with little success.
But those efforts gained renewed energy following a Jan. 8 intelligence briefing that congressional Democrats and two Republican senators said did not sufficiently inform Congress of the administration's strategy in the Middle East.
Republican Senators Rand Paul and Mike Lee said the briefing on Trump's engagement with Iran following the drone attack on Soleimani was among the worst they had been given during their time in the U.S. Senate.
Kaine won their support for the resolution along with votes from Republicans Susan Collins, Todd Young and Jerry Moran to attain the majority needed to pass the legislation.
Senate action on the war powers resolution follows a number of votes in the House of Representatives aimed at addressing rising tensions with Iran.
In January, House Speaker Nancy Pelosi acknowledged Soleimani was a terrible person, while stressing the importance of congressional debate over war powers.
The House voted nearly along party lines on January 9, passing a non-binding resolution similar to Kaine's legislation by a 224-194 vote.
Representative Elissa Slotkin, a Democrat who co-sponsored the legislation, said in a House floor speech, "If our loved ones are going to be sent to fight in any protracted war, the president owes the American public a conversation. The resolution we will be voting on today allows us to start that debate as our founders intended."
Later in the month, a pair of bills limiting Trump's military authority passed the House with some Republican support. The first bill limits funding for overseas military action if the president has not sought congressional approval for his or her actions.
The second bill repealed the 2002 Authorization of Military Force (AUMF) resolution that has been broadly used by presidents of both parties to justify U.S. military actions overseas. Trump, in part, used the 2002 AUMF to justify his strike against Soleimani, also citing an imminent threat to U.S. personnel overseas.
The White House said Trump would veto both of the House-passed measures if they also are approved by the Republican-majority Senate.
The U.S. Constitution gives Congress the sole responsibility to formally declare war. But American presidents have had wide latitude to unilaterally order military action in response to imminent threats and sudden crises.