McCain will never convince the conservative base (or at least enough to win an election) because of these issues:
1. McCain-Kennedy Immigration Amnesty Bill
2. McCain-Feingold Anti-First Amendment Bill
3. Gun Grabbing history
4. Gang of 14
5. Keating Scandal
6. Homosexual marriage/civil unions
7. Embryonic Stem Cell research
8. His 2000 outburst toward the Christian Right
9. His Giuliani-esque philandering while married
10. His hot uncontrollable filthy-mouth temper
I believe he may also be a global warmist. If the Republicans nominate McCain, so many conservatives will stay home in disgust that you may see 435 Democrats in the House of Representatives next January.