(CNN) - Sen. Barack Obama kicked off a multi-day bus tour in Pennsylvania Friday with a key endorsement and lingering controversy over his former pastor's racially sensitive comments.
Pennsylvania Sen. Bob Casey announced his support of Obama's White House bid on Friday at an event in Pittsburgh, Pennsylvania. It's an endorsement that could give the Illinois senator a boost in the crucial primary state that votes April 22.
"He started this campaign as an underdog, but he knows what it's like to be a fighter," Casey said. "I've been impressed by so much watching this campaign ... impressed by his compassion, his strength, his ideas and I think especially ... under fire."
Casey told the crowd that he called Sen. Hillary Clinton on Thursday night to inform her of the decision. "She was gracious ... and we know that she's a great senator, she's a great leader," Casey added.
Obama accepted Casey's endorsement, saying "Bob is such gracious person. I did not press him on this endorsement. There are others I press," he said.
He said Casey's endorsement "meant more to me as any endorsement I've received on the trail because I knew it was coming from the heart."