As many as 10 Republican senators are considering bucking President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE on a resolution that would limit his ability to take military action against Iran.

The increasing number is the latest sign of growing GOP frustration over the Trump administration’s justification for the drone strike that killed Iranian Gen. Qassem Soleimani.

Sen. Tim Kaine Timothy (Tim) Michael KaineBiden promises Democratic senators help in battleground states Second GOP senator to quarantine after exposure to coronavirus The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep MORE (D-Va.) is circulating a bipartisan resolution that would direct Trump to remove U.S. forces from any hostilities against Iran within 30 days of its enactment.

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GOP Sens. Mike Lee Michael (Mike) Shumway LeeMcConnell shores up GOP support for coronavirus package McConnell tries to unify GOP Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump MORE (Utah) and Rand Paul Randal (Rand) Howard PaulSecond GOP senator to quarantine after exposure to coronavirus GOP senator to quarantine after coronavirus exposure The Hill's Morning Report - Sponsored by National Industries for the Blind - Trump seeks to flip 'Rage' narrative; Dems block COVID-19 bill MORE (Ky.) have already voiced their support for the measure, and Kaine says about eight more Republicans, including Sens. Susan Collins Susan Margaret CollinsThe Hill's Campaign Report: Biden asks if public can trust vaccine from Trump ahead of Election Day | Oklahoma health officials raised red flags before Trump rally Gideon leads Collins by 12 points in Maine Senate race: poll Senate leaders quash talk of rank-and-file COVID-19 deal MORE (Maine), Lisa Murkowski Lisa Ann MurkowskiGOP ramps up attacks on Democrats over talk of nixing filibuster OVERNIGHT ENERGY: House Democrats tee up vote on climate-focused energy bill next week | EPA reappoints controversial leader to air quality advisory committee | Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' House Democrats tee up vote on climate-focused energy bill next week MORE (Alaska), Todd Young Todd Christopher YoungSenate GOP eyes early exit Why the US should rely more on strategy, not sanctions Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump MORE (Ind.) and Mitt Romney Willard (Mitt) Mitt RomneyGOP-led panel to hear from former official who said Burisma was not a factor in US policy Joe Biden's dangerous view of 'normalcy' The electoral reality that the media ignores MORE (Utah), are reviewing it.

“Probably about 10,” Kaine said when asked about the number of Republicans who could vote to rein in Trump’s powers. “There’s good discussion going on.”

Lee said several Republicans are carefully weighing whether to back the measure, adding that it “would not be unreasonable to say that there might be a group of 10 who should be considered potential candidates to vote for it.”

Democrats can force a vote on the measure at any time, but Senate Minority Leader Charles Schumer Chuck SchumerMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security Warren, Schumer introduce plan for next president to cancel ,000 in student debt Schumer lashes out at Trump over 'blue states' remark: 'What a disgrace' MORE (D-N.Y.) on Monday said a vote will happen later in the week.

Schumer wants to make sure his entire caucus is present, increasing the odds that a vote would be held sometime after Tuesday night’s Democratic presidential primary debate in Iowa.

It needs only a simple majority to pass.

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If it passes the Senate, the House would also need to pass the resolution before it can be sent to the White House, where Trump would be expected to veto it.

Lee said fellow Republicans should view the Kaine-sponsored resolution as a “completely noncontroversial measure” that restates the Constitution’s declaration that Congress shall have sole power to declare war.

He said it merely spells out that “additional hostilities against Iran need to be authorized by Congress.”

“That is a perfectly unremarkable statement,” Lee added. “The fact that this would be objectionable to anyone in either political party is really saying something.”

Republican senators are suggesting changes to Kaine’s resolutions, which the Democratic senator says can be offered as amendments on the Senate floor.

“I want to make sure that anything I vote on makes clear that the president maintains his Article II prerogatives and also that it does not contain any political content,” Young told reporters Monday, referring to Trump’s constitutional power to respond to attacks or imminent threats.

Kaine has agreed to accept Republican amendments that remove specific reference to Trump or might be construed as forcing the withdrawal of U.S. troops from areas where Iranian proxies are present.

Senate Republicans have been leery to criticize Trump publicly or to oppose him on highly political, high-profile votes.

GOP lawmakers, however, have shown more willingness to defy Trump when it comes to preserving Congress’s powers, particularly when it comes to declarations of war and appropriations.

Seven Senate Republicans voted in March to direct Trump to withdraw U.S. forces from supporting a Saudi-led coalition fighting in Yemen’s civil war, a resolution that Trump later vetoed and Congress failed to override.

Eleven GOP senators voted with Democrats in September to terminate a national emergency declaration Trump used to justify shifting military funds to construction of the border wall without congressional consent. Twelve GOP senators voted for a similar resolution in March.

Senators in both parties say a briefing by senior administration officials last week failed to provide a clear legal justification for the U.S. drone strike that killed Soleimani.

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The murky legal arguments put forth by the administration come on top of an evolving story about whether U.S. personnel in the Middle East faced an imminent threat from Soleimani, as Trump claimed last week when he said Iran and its allies “were looking to blow up our embassy.”

Secretary of State Mike Pompeo Michael (Mike) Richard PompeoHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers Treasury Dept. sanctions Iranian government-backed hackers The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep MORE on Friday also asserted “an imminent threat,” adding the intelligence included “attacks on U.S. embassies.” He declined to define what exactly he meant by imminent.

Defense Secretary Mark Esper Mark EsperTop admiral: 'No condition' where US should conduct nuclear test 'at this time' Overnight Defense: Trump hosts Israel, UAE, Bahrain for historic signing l Air Force reveals it secretly built and flew new fighter jet l Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' Oldest living US World War II veteran turns 111 MORE over the weekend told CBS’s “Face the Nation” that he “didn’t see” a “specific piece of evidence” that Soleimani was masterminding an attack on as many as four U.S. embassies.

The president pulled back from his initial claim on Monday by arguing that “it doesn’t really matter” whether there was an imminent threat against U.S. personnel and that the strike against Soleimani was justified “because of his horrible past.”

U.S. forces in the region were on high alert after the strike, and Iran’s Supreme Leader Ayatollah Ali Khamenei vowed “forceful revenge” against the United States.

Retaliation came in the form of 16 missiles fired by Iran at two Iraqi bases housing U.S. personnel, causing damage but resulting in no casualties.

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Iran then sent word to the Trump administration through Swiss intermediaries that it would not seek to further escalate hostilities.

“Iran appears to be standing down, which is a good thing for all parties concerned and a very good thing for the world,” Trump said Wednesday as lawmakers in both parties breathed a sigh of relief.

But Schumer and other Democrats warned on Monday that Iran could still retaliate.

“Iran can strike us in other ways in the months ahead, through cyber warfare, proxies or established terror networks that have destabilized the Middle East for decades,” Schumer said, adding that Khamenei warned the retaliatory missile strike was just “one slap.”

“The Senate must not allow the president to proceed unchecked. Sen. Kaine’s war powers resolution is needed now more than ever,” Schumer argued.

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellMcConnell focuses on confirming judicial nominees with COVID-19 talks stalled McConnell accuses Democrats of sowing division by 'downplaying progress' on election security Warren, Schumer introduce plan for next president to cancel ,000 in student debt MORE (R-Ky.) took to the Senate floor Monday afternoon to argue that Trump’s order against Soleimani was justified.

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He pointed to protests within Iran against the government over the unintentional downing of a Ukrainian airliner, which some Democrats have suggested was caused by heightened tensions between Washington and Tehran.

“Thousands of Iranians have taken to the streets to celebrate Soleimani’s death, condemn the regime’s domestic repression, call for regime change in Tehran,” McConnell said.

“I look forward to hearing my colleagues who want to quibble over the word ‘imminent’ explain just how close we should let terrorists come to killing more Americans before we defend ourselves,” he added. “I assure you, if the president had not acted to disrupt a deadly attack, I’m confident these same critics would have blasted him for failing to protect American lives.”

Jordain Carney contributed.