Following a number of Democrats, freshman Senator Joe Donnelly of Indiana says he now supports marriage equality for gay and lesbian couples.The Friday announcement comes days after other Democratic senators such as Bob Casey of Pennsylvania and Tom Carper of Delaware came out in support of gay marriage. Fellow freshman Democratic Senator Heidi Heitkamp of North Dakota also said she now favors same-sex unions.A petition launched by MoveOn.org this week urged Donnelly to rethinkhis views, and just last week a spokesperson told WFPL the Indiana Democrat was steadfast that such unions were reserved for a man and a woman only.From Donnelly's Facebook page: "In recent years, our country has been involved in an important discussion on the issue of marriage equality. While serving in the House of Representatives, I had the opportunity to act on a core belief of mine: we are a stronger country when we draw on the strengths of all Americans. I voted to repeal ‘don't ask, don't tell’ and was an original supporter of the bill that would make it illegal to discriminate against someone in the workplace because of their sexual orientation. It is also for that reason that I oppose amending either Indiana’s or our nation’s constitution to enshrine in those documents an ‘us’ and a ‘them,’ instead of a ‘we.’ With the recent Supreme Court arguments and accompanying public discussion of same-sex marriage, I have been thinking about my past positions and votes. In doing so, I have concluded that the right thing to do is to support marriage equality for all."According to gay rights advocates and their allies, four Democratic senators have yet to publicly endorse gay marriage: Tim Johnson of South Dakota, Mark Pryor of Arkansas, Joe Manchin of West Virginia and Mary Landrieu of Louisiana.