Vice President Joe BidenJoseph (Joe) Robinette BidenObama tweets birthday message to Biden: 'The best vice president anybody could have' The Hill's 12:30 Report Tech beefs up lobbying amid Russia scrutiny MORE couldn't say on Tuesday whether President Barack ObamaBarack Hussein ObamaReport: FCC chair to push for complete repeal of net neutrality Right way and wrong way Keystone XL pipeline clears major hurdle despite recent leak MORE would make another trip to Pennsylvania to campaign on behalf of Sen. Arlen Specter (D).

Biden said that while he planned to campaign alongside Specter, who's facing a tough primary election next Tuesday against Rep. Joe Sestak (D), he couldn't say whether the president's schedule would permit Obama to make such a trip.

"He already has gone out and campaigned for Arlen Specter," Biden noted on NBC's "Today" show when asked if Biden would travel to Pennsylvania again to campaign for Specter.

Obama had endorsed Specter's reelection after the veteran senator switched from being a Republican to run for reelection as a Democrat, handing his new party a 60-vote, filibuster-proof Senate majority for a short time. A number of other top Democrats backed Specter in the immediate aftermath of his party switch.

But Sestak has waged a vigorous campaign against Specter over the past few months, and recent polls suggest that he's either within striking distance -- if not ahead -- of Specter with only a week left.

"The president, I'm sure, will be reaching out," Biden said. "Whether the president's going to go up there physically again between now and Tuesday, I don't know the schedule."

Obama has made some high-profile campaign stops for Democratic candidates who ended up going down to defeat, most notably Massachusetts Attorney General Martha Coakley, who lost to Sen. Scott Brown (R) in the state's special election.