Despite frequent claims to the contrary, John McCain is unlikely to win the GOP presidential nomination in 2008 for one simple reason: the conservative establishment, which controls the Republican Party, hates him. It's the same reason he lost in 2000.
Here's a leading indicator -- anti-McCain vitriol from top apparatchik Grover Norquist:
Sen. John McCain (R-Ariz.) became a target in the latest round of political rhetoric when Republican strategist Grover Norquist referred to him last week as "the nut-job from Arizona...
Norquist said he "misspoke" and added, "I meant to say gun-grabbing, tax-increasing Bolshevik."
(For more on how the party establishments have re-established control over the primary process, see this 2004 paper by Marty Cohen, David Karol, Hans Noel and John Zaller [PDF].)