Vice President Joe Biden appeared in a radio ad for Sen. Arlen Specter (D-Pa.), calling him "an amazing guy."

In the one-minute spot, Biden praises the "depth of his scholarship, his gumption."

"This guy is a guy with more steel in his backbone than most people have in their whole body," Biden says of Specter.

Biden, a Pennsylvania native, urged voters to keep the five-term senator in office, reminding them of Specter's seniority in the Senate.

"Pennsylvania, to lose that seniority, to lose that fight, to lose that tenacity, this guy never gives up. He's just an amazing guy," Biden says.

Biden was in Pennsylvania in April to campaign for the Republican-turned-Democrat senator. He also helped convince Specter in 2009 to change parties.

Specter faces a tough primary challenge from Rep. Joe Sestak (D-Pa.). Most polls show the race is too close to call, although a Suffolk University poll out Wednesday showed Sestak with a 9-point lead.

Meanwhile, our colleague Alexander Bolton reports Specter doesn't think his past vote against Supreme Court nominee Elena Kagan will be an issue in Tuesday's primary election.

“There are so many things that are putting me in a tough position politically that I wouldn’t say that it even gets on the scoreboard,” Specter said.

Sestak has attacked Specter for voting against Kagan last year for her post as solicitor general.
Specter defended his vote, which he cast while still a member of the Republican Party.
“Every move I make, he’s trying to politicize,” Specter said of his opponent. “He might want to rush to judgment and make a decision before a hearing, before knowing what the facts were, but I take these things very seriously.”