Mark Critz, a former aide to the late John Murtha and the Democratic nominee to replace him, has pulled out to a 6-point lead in the special election for Pennsylvania's 12th district, according to a new Susquehanna poll. Critz leads Republican Tim Burns 44%-38% with less than a week to go.

The Johnstown-based district in southwestern Pennsylvania has swing potential, despite the overwhelming Democratic registration advantage and Murtha's dominance in the district for the last 36 years. It's the only district that voted for both John Kerry and John McCain.

Critz is running as a continuation of Murtha -- a strategy that could be detrimental to his chances, as we've seen two incumbents in the last several days lose the nomination of their own party. And two more incumbents are in danger next Tuesday, as well, as Sens. Arlen Specter (D-Pa.) and Blanche Lincoln (D-Ark.) go up against formidable challengers.

Both national parties are spending big on this race, as it could provide a boost in momentum for either. That includes Republicans, who haven't won a competitive House special election this cycle.

The survey was conducted May 10 of 400 likely voters with a margin of error of +/- 4.9%.