The Second Term Jinx
I'm afraid I must invoke Andersen's Modifier(*) on the emerging story about how second term presidents "are often plagued by scandals". While it is true that Nixon, Reagan and Clinton all had serious scandals during their 2nd terms, can anyone recall the serious scandal that plagued Eisenhower's second term?
Like the Redskin rule, these kind of coincidences are interesting fodder for water-cooler talk, but they are not the kind of thing we should take political comfort in. We must assume that Bush will have a relatively easy-go of it in the next four years and plan our course of action with that idea in mind. We must assume that we will have to defeat a Republican party riding high on the successes of four more years of Bush.
If we assume Bush will succeed we'll be all the better prepared to handle him when he inevitably fails.
(* - Though, admittedly, it doesn't apply perfectly since the question of what happens in a second term is political in nature. The Modifier is just a special case of the general rule that correlation does not equal causation.)