(Bloomberg) -- The Senate is holding a marathon vote on a bill requiring President Donald Trump to seek congressional approval for any military action in Iran -- one of the few measures considered by the Republican-led chamber to curtail his war-making ability.Voting on the measure began just after 5 a.m. Friday with 45 votes in favor and 41 votes opposed by midday. The vote could stay open into the night to allow the six senators running for president to fly back from the Democratic debates in Miami.Senate Majority Leader Mitch McConnell allowed the vote, even though it was difficult to schedule. It needs 60 yes votes to pass, something McConnell predicted would not happen.The legislation would be included as an amendment to the National Defense Authorization Act, a massive annual spending bill that is one of Congress’s few must-pass priorities. It would restrict the use of funds authorized by the act from being used “to conduct hostilities against the government of Iran, against the armed forces of Iran, or in the territory of Iran,” unless authorized by Congress.“Dictators and kings declare war unilaterally, not democracies,” Tom Udall, a New Mexico Democrat and the lead sponsor of the amendment, said on the Senate floor. “The people decide whether we go to war or whether we don’t go to war through their elected representatives. Congress is the most direct voice of the people.”‘Real Sacrifices’The measure has narrow bipartisan support from two Republican co-sponsors: Senators Rand Paul of Kentucky and Mike Lee of Utah. Even so, the measure is expected to fall short of the 60-vote threshold needed for passage.But for Udall and other supporters of the measure, there is value in having the debate and putting senators on the record.“Our troops will be the ones making real sacrifices,” Udall said. “We can bear the cost of some inconvenient recess travel. Our job is to debate and vote on matters of war and peace, period, end of story.”Senator Tim Kaine of Virginia, one of the Democratic co-sponsors of the measure and a member of the Foreign Relations Committee, said his pitch to his Republican colleagues would be that they “should vote for their own power.”“You should not outsource this congressional responsibility to any president of any party,” Kaine said in an interview. “You should jealously guard it. And you should guard this prerogative like others.”The Senate passed the underlying NDAA on Thursday, but Republicans and Democrats agreed to vote on the amendment throughout the day Friday.(Updates to add ongoing vote count beginning in the second paragraph.)\--With assistance from Travis Tritten.To contact the reporter on this story: Daniel Flatley in Washington at dflatley1@bloomberg.netTo contact the editors responsible for this story: Joe Sobczyk at jsobczyk@bloomberg.net, Laurie Asséo, Anna EdgertonFor more articles like this, please visit us at bloomberg.com©2019 Bloomberg L.P.