WASHINGTON (AP) — The Senate is headed toward a vote Wednesday on President Donald Trump's decision to embark on a war against Iran, an extraordinary test in Congress for a conflict that has rapidly spread across the Middle East with no clear U.S. exit strategy.

The legislation, known as a war powers resolution, gives lawmakers an opportunity to demand congressional approval before any further attacks are carried out. The Senate resolution and a similar bill being voted on in the House later this week face unlikely paths through the Republican-controlled Congress and would almost certainly be vetoed by Trump even if they were to pass.

Nonetheless, the votes marked a weighty moment for lawmakers. Their decisions on the five-day-old war — which Trump entered without congressional approval — could determine the fates of U.S. military members, countless other lives and the future of the region.

“Today every senator — every single one — will pick a side," said Senate Democratic Leader Chuck Schumer during a floor speech. “Do you stand with the American people who are exhausted with forever wars in the Middle East or stand with Donald Trump and Pete Hegseth as they bumble us headfirst into another war?”

Trump administration scrambles for congressional support

After launching a surprise attack against Iran on Saturday, Trump has scrambled to win support for a conflict that Americans of all political persuasions were already wary of entering. Trump administration officials have been a frequent presence on Capitol Hill this week as they try to reassure lawmakers that they have the situation under control.

Defense Secretary Pete Hegseth said Wednesday that the war could extend eight weeks, a longer time frame than has previously been floated by the Trump administration. He also acknowledged that Iran is still able to carry out missile attacks even as the U.S. tries to control the country's airspace.

U.S. service members “remain in harm’s way, and we must be clear-eyed that the risk is still high,” Gen. Dan Caine, chairman of the Joint Chiefs of Staff, said at the same press conference.

Six U.S. military members were killed over the weekend in a drone strike in Kuwait.

Trump has also not ruled out deploying U.S. ground troops. He has said he is hoping to end the bombing campaign within a few weeks, but his goals for the war have shifted from regime change to stopping Iran from developing nuclear capabilities to crippling its navy and missile programs.

Sen. John Barrasso, second in Senate Republican leadership, said GOP senators would send a message that Democrats are “wrong” for forcing a vote on the war powers resolution.

“Democrats would rather obstruct Donald Trump than obliterate Iran's national nuclear program,” he added.

Almost all Republican senators were readying to vote Wednesday against the war powers resolution to halt military action, but a number still expressed hesitation at the idea of troop deployments.

“I don’t think the American people want to see troops on the ground,” said Sen. Bill Cassidy, R-La., as he exited a classified briefing Tuesday. He added that Trump administration officials “left open that possibility,” but it wasn't an option they were emphasizing.

Republican Sen. Todd Young, who told reporters earlier this week he was undecided on the legislation, released a statement Wednesday morning saying that now that the U.S. has entered the war, the danger "will only grow if we limit the president's military options at this critical moment."

He called for lawmakers to conduct oversight and evaluate any requests from the administration for more wartime funding or authorities.

Lawmakers to go on record

The votes in Congress this week represented potentially consequential markers of just where lawmakers stand on the war as they look ahead to midterm elections and the consequences of the conflict.

“Nobody gets to hide and give the president an easy pass or an end-run around the Constitution,” said Sen. Tim Kaine, the Virginia Democrat leading the war powers resolution. “Everybody's got to declare whether they're for this war or against it.”

Republican leaders have successfully, though narrowly, defeated a series of war powers resolutions pertaining to several other conflicts that Trump has entered or threatened to enter. This one, however, is different.

Unlike Trump's military campaigns against alleged drug boats or even Venezuelan leader Nicolás Maduro, the attack on Iran represents an open-ended conflict that is already ricocheting across the region. For Republicans who are used to operating in a political party dominated by Trump and his promises of keeping the U.S. out of foreign entanglements, the moment represented a bit of whiplash.

“War is ugly, it always has been ugly, but we're taking out a regime that has been trying to attack us for quite some time,” said Sen. Markwayne Mullin, an Oklahoma Republican.

Meanwhile, Sen. Lindsey Graham, a South Carolina Republican who has long pushed Trump to engage overseas, argued that the widening conflict represented an opportunity for Arab and European countries to join in the fight against Iran and the militant groups it supports.

“I don’t mind people being on record as to whether or not they think this is a good idea,” he told reporters, but also argued that too much power over the military was ceded to Congress in the War Powers Act, which mandates that presidents must withdraw troops from a conflict within 90 days if there is no congressional authorization.

House vote looms

On the other side of the Capitol, House leaders were also readying for an intense debate over the war followed by a vote Thursday.

“I do believe we have the votes to defeat it, I certainly hope we do,” House Speaker Mike Johnson said after an all-member briefing on Tuesday night. Republican leaders were pushing to the floor their own counter-programming resolution that states that Iran is ”the largest state sponsor of terrorism."

Meanwhile, House Democratic leader Hakeem Jeffries said he expected a strong showing from Democrats in favor of the war powers resolution. At a news conference Wednesday, several Democratic members who are veterans of the Iraq and Afghanistan wars spoke about the heavy costs of those conflicts.

One of them was Rep. Jason Crow, D-Colo. “I learned when I was fighting in Iraq and Afghanistan, that when elites in Washington bang the war drums, pound their chest, talk about the costs of war and act tough, they're not talking about them doing it, they're not talking about their kids,” Crow said. “They're talking about working class kids like us.”