As the title says; what if George W Bush doesn't run in 2000 (McCain gets the nomination instead, presumably), and for whatever reason, Jeb Bush runs in 2004?
How will national politics be changed by George Jr's refusal to run in 2000, how could events be arranged to get Jeb as a serious contender in an alt-2004, and how will other issues be different (whether McCain or Gore wins in 2000)?
For that matter, what kind of campaign could Jeb be likely to run?