Watch Sen. Casey's interview with Wolf Blitzer.

WASHINGTON (CNN) -– Pennsylvania Sen. Bob Casey, Jr., a supporter of Sen. Barack Obama, is defending the Illinois senator and front-runner for the Democratic presidential nomination in the middle of a controversy that has the potential to effect the outcome in Pennsylvania's April 22 primary. (Related video: Watch John King on the potential impact of the controversy.)

“Ridiculous,” is how Casey responded to suggestions that Obama is an elitist. “Anyone who knows Barack Obama, knows his life story, knows that that’s not true,” Casey added.

“Here’s the larger point,” Casey told CNN’s Wolf Blitzer on Late Edition Sunday. “He was trying to express the frustration that people feel not only with this economy but with what’s been happening in Washington where the special interests have had a stranglehold on the process in Washington.”

Casey also took a shot at Sen. John McCain, the Republican Party’s presumptive nominee, saying “the McCain campaign is about a third Bush term.” “I don’t think people are going to vote for that. I think they’re going to vote for change,” said Casey.

The Pennsylvania senator also told Blitzer that people in his state are not going to judge Obama on the basis of a single comment.

Related video: Bayh on Obama

–CNN Associate Producer Martina Stewart

Watch Casey endorse Obama Friday.

(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."

Casey will endorse Obama Friday.

(CNN) — Pennsylvania Sen. Bob Casey will announce his support of Barack Obama's White House bid Friday, an endorsement that could give the Illinois senator a boost in the crucial primary state that votes April 22.

The official endorsement is expected to come later Friday as Obama begins a week-long campaign-swing through the state. Several recent polls suggest Hillary Clinton appears to hold a double-digit lead there.

Casey is a first-term senator and son of a popular former governor of the state, Bob Casey, Sr. A prominent catholic, Casey's support could help Obama make inroads among catholic voters in the state — a voting bloc that has favored Clinton in most other primary contests.

In 2002, Casey lost a hard-fought gubernatorial primary contest against Pennsylvania Gov. Ed Rendell, now an ardent supporter of Hillary Clinton's White House bid.

– CNN Ticker Producer Alexander Mooney