The 2004 United States Senate election in Pennsylvania was held on November 2, 2004. Incumbent Republican Senator Arlen Specter won re-election to a fifth term. As of 2026, this is the last time a Republican statewide candidate won Montgomery and Delaware Counties and won more than 25% of the vote in Philadelphia. Specter later lost renomination in 2010 as a Democrat, having joined the party in April 2009. Specter’s party switch marked the first time since 1947 that Democrats held both of Pennsylvania’s U.S. Senate seats.
Democratic primary
Campaign
Democrats had difficulty recruiting top tier candidates against the popular Specter. Among the Democrats to decline to run for the nomination were Treasurer (and former Republican) Barbara Hafer, Public Utilities Commissioner John Hanger, real estate mogul Howard Hanna, State Representative (and also former Republican) John Lawless, and State Senator (and future Congresswoman) Allyson Schwartz.
Congressman Hoeffel ended up running unopposed for the Democratic nomination. Software businessman Charlie Crystle was considered a strong possible candidate, but he dropped out before the election.
Republican primary
Campaign
Specter faced a primary challenge from Representative Pat Toomey. Despite the state Republican Party's strong history of embracing a moderate philosophy, the influence of conservatism among rank-and-file members had been steadily growing for decades; because of his liberal social views, Specter was often considered to be a "Republican in Name Only" by the right. Although Specter had a huge fundraising advantage, Toomey was aided by $2 million of advertising from the Club for Growth, a conservative political action committee that focuses on fiscal issues and targets moderate Republican incumbents. Toomey criticized Specter as a spendthrift on economic policy and as out of touch with his own party on social issues. Although Toomey had difficulty with name recognition early in the campaign, he built huge momentum over the final weeks preceding the primary, and Specter appeared to have transitioned from having a comfortable lead to being behind his challenger.
Specter received a huge boost from the vocal support of President George W. Bush; most of the state's Republican establishment also closed ranks behind Specter. This included Pennsylvania's other U.S. Senator, Rick Santorum, who was noted for his social conservative views. Many Republicans at the state and national level feared that if Toomey beat Specter, he wouldn't be able to defend the seat against his Democratic opponent.
Results
The results were much closer than analysts expected, with Specter narrowly winning by a margin of 1.64%. Specter's percentage of the vote was spread evenly across the state, and he received the most votes in the suburban counties of Montgomery, Chester, and Delaware.
Meanwhile, Toomey dominated in his home region of the Lehigh Valley, which he represented as a congressman from Allentown, winning Lehigh and Northampton by wide margins. Toomey also did well in Western Pennsylvania and Metro Pittsburgh, where suburban voters (who turned out the most in primaries) tended to be more socially conservative.
General election
Candidates
Major
- Joe Hoeffel (D), U.S. Representative
- Arlen Specter (R), incumbent U.S. Senator
Minor
- Jim Clymer (C)
- Betsy Summers (L)
Campaign
For Democrats, hope of winning the election centered on Toomey's defeat of Specter. However, after the challenge from the right failed, enthusiasm from the party establishment waned and Hoeffel had difficulty matching the name recognition and fundraising power of his opponent Despite contempt from conservatives, Specter enjoyed high levels of support from independent voters and, as in previous elections, a surprisingly large crossover from Democratic voters. Even in the areas in which Toomey performed best in the Republican primary (mainly the state's conservative, rural center), Specter performed well. Except for his large margin of victory in almost uniformly Democratic Philadelphia, Hoeffel was crushed at the polls; his only other wins came by close margins in three metro Pittsburgh counties; although President Bush proved to be unpopular in the state, voters were not willing to abandon Specter over party affiliation. Incidentally, Toomey was elected to the seat in 2010, after Specter switched to the Democratic Party in 2009 and subsequently lost renomination to U.S. Congressman and former Navy Admiral Joe Sestak.
Endorsements
Joe Hoeffel (D)
Arlen Specter (R)
Results
Counties that flipped from Republican to Democratic
- Alleghany (largest city: Pittsburgh)
- Beaver (largest city: Beaver)
- Fayette (largest borough: Uniontown)
Counties that flipped from Democratic to Republican
- Somerset (largest city: Somerset)