Recent history would say that a Republican will win. Just over the last 100 years, a party hanging on after 8 years only happened twice if you throw out the FDR years as an aberration. Hoover and Bush I are the only ones to pull that off. Nixon couldn't do it in 1960, not Humphrey in '68, Ford in '76, Gore in '00 or McCain in '08.
True, but those elections didn't have one party dominated by wingnuts