2008
Knowing that Obama will kill bin Laden, pass RomneyCare and that the economy will continue to collapse in 2009, only to emerge in a state of stasis by the end of 2010. Further, the Tea Party will be popular only to lengthen the slow down with a wave of job-killing, credit-freezing austerity measures.
2004
Knowing that the Iraq war will take another 5 years and 3000 casualties under Bush and that Bush's ownership society will cause the economy to crash in 2007 and not recover in the foreseeable time thereafter.
2000
Knowing about the enite Bush v. Gore, and America's lost decade. See 2004.
Should be higher, but the Rovian machine prevents any second or third tier battlegrounds from forming.
1996
Knowing how strong the late 90s will be and how sleezy the GOP congressional machine will operate will give Clinton some extra strength.
1992- same as 1996, but Clinton will have to explain why he gets nothing done and loses congress in 1994.
1988- Well, we know now more than then that the Soviets would turn out to be incompetent (though the Soviet Union was already beginning to unravel). Bush's involvement in Iraq would hurt him for though he dealt with Saddam in the short term, we know now that it invited HW's son to the biggest military mindphuck since Vietnam. This would be a big thing since HW basically won by painiting Dukakis as a pussy. Also, Reaganomics would soon learn its limits with a slowdown around 1991 and that Bush would break his own promises to not raise taxes and concede on an issue that must have been very dear to him. We know now that Bush was basically the Carter-lite of the right. The election would have been like 2000 or 2004.
Bush 49.8% 278 EVs
Dukakis 48.9% 260 EVs
1984- We now know that the late 80s were time of cocaine, champagne and parachute pants. What a party. Iran-Contra would be seen as the only real negative and any bad consequences of Reaganomics we face today would be acknowledged only in the face of what we were then getting out of. Also, we now know that only Reagan could of saved the world from communism without a nuclear holocaust.
This is what would happen-
Same goes for 1980.
However, hindsight would have prevented the abominations known as the Nixon Administration and Carter Administration. Though I suspect that a Huphrey Administration would lose in 1972 from Democrat Fatigue and Carter would have lost to whoever won in 1976, provided they were not frauds and burglars.