Washington (CNN) - Vice President Joe Biden heads to Pennsylvania Friday to lend a hand to two fellow Democrats.
Friday morning Biden headlines a fundraiser in Pittsburgh for Mark Critz, the Democratic candidate in the May 18 special election to fill the seat of the late Rep. Jack Murtha, a Democratic source tells CNN.
Critz, a longtime aide to the late congressman, is facing off against Republican Tim Burns. The race has heated up in recent weeks, with both campaigns as well as national party committees going up with television ads.
The district, which stretches from Cambria County in west-central Pennsylvania down to the southwestern corner of the state, is considered socially conservative. In the 2004 presidential election, Sen. John Kerry won the district by 2 points. Sen. John McCain narrowly edged out Barack Obama in the district in 2008, even though Obama carried the state by 10 percent.
Following the fundraiser, the vice president heads east, where he'll be the main attraction at a rally for Sen. Arlen Specter. The event, Friday afternoon at the Wilkes-Barre/Scranton International Airport, brings Biden close to his native Scranton for the first time since becoming vice president.
Specter, a Republican turned Democrat, is facing a tough re-election as he fights for a sixth term in the Senate. Before reaching the general election against former Rep. Pat Toomey, Specter must first defeat Rep. Joe Sestak in the May 18 Democratic primary.
Sestak, a former admiral in the Navy, has written a letter to Biden asking the vice president to call for an end to Specter's "baseless attacks on Joe's distinguished career in the United States Navy," according to a press release.
In a Specter campaign commercial released Tuesday, an announcer says "Joe Sestak – relieved of duty in the Navy for creating a 'poor command climate.'" The ad also accused Sestak of missing 127 votes in the House, "the worst attendance of any Pennsylvania congressman."
In response, the Sestak campaign accused Specter of launching a Republican-style negative campaign in his TV ads
According to a recent Quinnipiac University poll, Specter holds a 53 to 32 percent advantage over Sestak in the Democratic primary matchup, with 15 percent undecided.
Next Friday, April 30, the vice president is expected to headline a fundraiser for Rep. Betsy Markey of Colorado, according to the Democratic source. The freshman Democrat faces a tough re-election bid this year, and has been targeted by Republicans for her vote in favor of her party's health care reform legislation. The next night Biden's the main attraction at a Democratic Party dinner in Arizona.
–Follow Paul Steinhauser on Twitter: @psteinhausercnn