Kerrey's residency, meanwhile, has already come up. In once release, the National Republican Senatorial Committee cast him as a "changed" candidate since living "in Greenwich Village for so many years."
It's similar to the charge Democrats tried to level against Sen. Dan Coats, R-Ind., who made a successful comeback bid in 2010. Democrats relentlessly pointed out that Coats had been registered to vote in Virginia, not Indiana. The attacks ultimately feel short as Coats cruised to victory in the wave year.
In addition to Coats, there are two other senators currently serving who waged successful comeback bids.
Sen. Frank Lautenberg, D-N.J., retired in 2000, only to jump back into the mix in 2002 when he made a bid to replace then-Democratic Senator Robert Torcelli, who was embroiled in a campaign finance scandal. Republican nominee Douglas Forrester tried to capitalize on Lautenberg's late entrance into the general election, and attacked the Senator for his 1991 vote against the Gulf War resolution.
He also lampooned Lautenberg's age -- 78 at the time -- questioning whether the New Jersey Democrat was too old to run for the seat. Still, with the national Democrats and state party behind him, Lautenberg easily won back a seat.
The other member of the Senate serving non-consecutive terms is Sen. Kent Conrad, D-Neb. Conrad, who was preparing to retire in 1992, but ended up running in a special election for North Dakota's other Senate seat following the death of Republican Sen. Quentin Burdick. For a few hours, Conrad technically held both North Dakota Senate seats.
--Sean Sullivan contributed