How conservative is John McCain? According to the influential American Conservative Union, the AZ senator rates lowest of all potential conressional GOP candidates in 2008. Here are their 2005 and lifetime scores with my assesment of the likelihood of their candidacy:

Tom Tancredo-100/99 (unlikely to run)
Sen. Sam Brownback-100/95 (may run, but won't get far; longshot for VP)
Rep. Duncan Hunter-92/92 (is running, but won't get far)
Newt Gingrich-NA/90 (may run late, but I'm guessing he won't)
Sen. Chuck Hagel-96/86 (unlikely to run)
Sen. John McCain-80/83 (has been running since 1999)

Other former potential candidates:
Sen. George Allen-100/92
Sen. Bill Frist-92/89

This means that McCain in 2005 was the 46th most conservative GOP senator (or the 10th most liberal).

The ACU doesn't rate governors and mayors.

Also, the president of the ACU-David Keene-had this to say about how pro-McCain Republicans could successfully win the nomination for their man:

"They don't have to get folks like me to love John McCain. They just have to get us to quietly grumble, rather than run around the country saying out loud that we just really don't want him."

I don't know about you, but I don't feel like quietly grumbling if that is going to be the consequence.