What if George W.Bush declined to run for president in 2000?

[Mr. Morden]

With no Bush in the race, folks like John Engler, Tommy Thompson, and Frank Keating would have run.  You would have seen a very crowded field.  Elizabeth Dole would have led the early polls because of name recognition.

[Mr. Morden]

There would be no reason for Paul to run if Bush hadn't, and Buchanan ran as the Reform Party's nominee (although didn't he start out in the GOP primaries?).

Yes, IRL, Buchanan started out running for the GOP nomination, but then dropped out of the race to switch to the race for the Reform Party nomination, around Oct. 1999 or so.

The race for the 2000 GOP nomination started out crowded (and would have been even more crowded if Bush hadn't run, and scared people out of the race), but by the end of 1999, half the field had dropped out.  If Bush hadn't run, it probably would have been the most crowded field in modern history, and would have been a really wild affair, since there wouldn't have been a single dominating frontrunner.