[cnn-photo-caption image= http://i.cdn.turner.com/cnn/2008/images/05/13/art.romer.ap.jpg caption="Romer, a former DNC chairman, endorsed Obama Tuesday."]
(CNN) - Barack Obama picked up endorsements from three more superdelegates Tuesday, extending his lead over Hillary Clinton in that category to seven.
Indiana Rep. Joe Donnelly, New Orleans Mayor Ray Nagin, and former Colorado Gov. and onetime Democratic National Committee Chairman Ray Romer have all announced they are backing the Illinois senator.
In a conference call with reporters, Romer acknowledged he has known both Clintons much longer than he has known Obama, but said he feels it is now impossible for the New York senator to win the nomination.
“There is a time we need to end it and direct ourselves to the general election. I think that time is now," he said.
According to CNN's tally, Obama now has the support of 280 superdelegates compared to Clinton's 273.