Factbox: U.S. Senate Democrats line up behind Iran nuclear deal

Democrat Barbara Mikulski provided the pivotal commitment to defending the deal negotiated by the United States and other world powers. The pact would put new limits on Iran's nuclear program while lifting sanctions on the country.

President Barack Obama needs the backing of 34 senators to ensure lawmakers cannot override a likely veto by him of a measure to disapprove the agreement. Counting Mikulski, 32 Democratic senators and two independents who vote with Democrats have pledged support for the deal.

The following describes how votes are likely to play out:

(Reporting by Patricia Zengerle, Susan Cornwell, Susan Heavey and Alex Wilts; Editing by Kevin Drawbaugh and Lisa Von Ahn)