The 2004 PA GOP Senate primary, a contest between Longtime Senator Arlen Specter and Lehigh Valley Congressman Pat Toomey resulted in the closest Primary win of Arlen Specter's 30 year Senate Career.
Never beloved By Conservatives, Toomey–––A Staunch Tax cuts and anti-abortion advocate–––sought to oust specter. However, he ran into issues as it was made clear to him that incumbent GOP President George Bush supported Arlen Specter for reelection.
Further, Specter ran on his experience, campaigning on a slogan of “Courage. Clout. Convictions” he argued in favor of his historic moderation as a means to achieve balance in the political system.
Simultaneously, he made regular appearances with the State's Junior Senator–––Rick Santorum–––as well as Vice President Dick Cheney & George W. Bush.
By Contrast Toomey ran on his conservative Bonafides
All of this ended up resulting in Specter winning by a narrow 51-49%, winning mainly thanks to the Philadelphia suburbs, Central PA, North Central PA, and Northeastern PA.
Toomey, however, nearly ousted Specter as he did well in Southwestern PA, Southcentral PA & had a fortuitously mighty showing in his home region of the Lehigh Valley