Factbox: Senate Democrats line up behind Iran nuclear deal

Sep 4 (Reuters) - Another U.S. senator declared support on Friday for the U.S.-led nuclear agreement with Iran, bringing to 38 the number who support the deal the same day a key Democrat said he would be a no vote. Senator Michael Bennet of Colorado said he backed the agreement, but Ben Cardin, the top Democrat on the influential Senate Foreign Relations Committee, announced he would be a no. The nuclear agreement between the United States, five other world powers and Iran announced on July 14 exchanges relief from crippling economic sanctions for Iran's agreement to curtail its nuclear program. President Barack Obama now has the support he needs in Congress to protect the deal. It takes 34 Senate votes to ensure lawmakers cannot override his promised veto of a measure to disapprove the agreement. But deal supporters had hoped to reach 41 Senate votes, enough to use the filibuster procedural rule to block a disapproval resolution and keep Obama from having to use his veto power. That prospect seems remote. A spokesman for Senator Joe Manchin, one of the five remaining undecided Democratic senators, said on Friday Manchin had not decided whether he would back the deal but would not support a filibuster. Under the "Iran Nuclear Review Act," which Obama signed into law in May, Congress has until Sept. 17 to vote on a resolution of disapproval. The legislation also provides 22 more days after that for Obama to veto the bill and Congress to try to override it. The following describes how votes are likely to play out: * When Congress returns on Sept. 8 from its long Augustrecess, debate will begin on a Republican-sponsored "resolutionof disapproval" against the deal. * In the Senate, the Republicans must gather 60 votes tomove the resolution forward under Senate procedural rules. Ifthey can, they will then need 51 votes to approve theresolution. * There is no similar procedural barrier in the House. Theresolution is expected to easily win approval there in a voteexpected next week. * If both chambers approve the resolution, it would go toObama's desk for review. He has vowed to veto it. * If he does, opponents would try to override the veto. Thiswould take a two-thirds majority in each chamber. The Senate has100 members; the House, 434, plus one vacant seat. * Democrats could block an override in the Senate with 34votes. So far, 38 senators have committed to back the deal. * In the House, if Republicans voted unanimously against thedeal, they would need to get at least 44 Democrats to vote withthem to override a veto. * If Congress were to pass a resolution of disapproval andoverride a veto, Obama would be barred from temporarily waivingmost of the U.S. sanctions imposed on Iran over its nuclearprogram. Proponents of the agreement argue that this would killthe deal. (Reporting by Patricia Zengerle; Editing by Kevin Drawbaugh, Lisa Von Ahn and Andrew Hay)