However, the biggest opponent in the 2000 GOP primary to W was McCain. Exclude him and is there a chance someone else takes his place and succeeds? The thing that sank McCain in SC was the rumor about his adopted daughter being an illegitimate black baby - what if someone less able-to-be-libeled beats Bush?
The smear campaign didn't just attack McCain's child, or his war record for that matter. Bush's men also made up lies that McCain's wife was a drug addict and that he was gay. This could have been done against any opponent. And to my knowledge, what was worse than the smear campaign was McCain's poor response to Bush's attacks. McCain retaliated by his own negative ad campaign that compared Bush to Bill Clinton, which did not endear him to Republican voters. In a TV debate he criticized Bush for going negative, only for Bush to pull out a negative ad that said "paid for by John McCain" at the bottom. Both moves made him look hypocritical. Also, his criticism of Bush's tax plan as a policy that would benefit the wealthy didn't help him in such a conservative state.
Aside from McCain, Bush's major opponents were Alan Keyes and Steve Forbes. I doubt either one would've beaten him in the primaries. Without McCain, Bush likely sails to the nomination. But it's possible that without the smear campaign against McCain, Bush does better with independents and he wins the popular vote in 2000.