Santorum was a sitting Senator, and lost reelection worse than Christine O’Donnell did in her infamous defeat, a history making 17.4% wipeout as an incumbent.
Santorum was a big Romney supporter in 2008, and endorsed presidential candidate Arlen Specter running on a platform of removing pro-life from the party platform in 1996.
Santorum has many similarities with Romney, such as having switched to pro-life for his first campaign, and being anti-Reagan during the Reagan years