According to Political Wire sources, former Rep. Ron Klink (D-PA), the Democratic candidate in 2000 against Sen. Rick Santorum (R-PA), will endorse incumbent Sen. Arlen Specter (R-PA) over his challenger, Rep. Joe Hoeffel (D-PA). The endorsement will be unveiled Thursday morning at a press conference Specter is holding to announce the formation of "Democrats for Specter."