President Barack Obama must navigate a treacherous course through Congress to prevent the U.S.-led international nuclear deal with Iran from being torpedoed. His goal is to get enough fellow Democrats to back the deal to offset nearly unanimous Republican opposition. Democratic Senator Brian Schatz of Hawaii said on Monday he backs the deal. Here's how upcoming votes on it are likely to play out: * Republicans broadly oppose the deal. They have majority control of the Senate and the House. Some Democrats have concerns about the deal, too. * When Congress returns from its August recess on Sept. 8, debate will begin on a Republican-sponsored "resolution of disapproval" against the deal. * In the Senate, Republicans must gather 60 votes to move the resolution forward through the Senate process. If they can get that, they will need only 51 votes to approve the resolution. They have until Sept. 17 to get that done. * There is no similar procedural barrier in the House. The resolution is expected to win approval there with ease. * If both chambers vote in favor of the resolution, it will go to Obama and he has vowed to veto it. * If he does, opponents would then likely try to override the president's veto. An override requires a two-thirds vote. The Senate has 100 members, the House has 435. * In the House, Republicans would need to be unanimous in their vote and win over at least 44 Democrats to override. So far, nine House Democrats have said they oppose the deal. * Democrats could block an override in the Senate with 34 votes. So far, 16 senators have committed to voting in favor of the deal; 16 others have vowed to opposed the deal.
