Andrew Sullivan sums it up:
So far, he has let us all down. My guess is he will continue to do so. And that decision, for my part, ends whatever respect I once had for him. On core moral issues, where this man knew what the right thing was, and had to pick between good and evil, he chose evil. When he knew that George W. Bush's war in Iraq was a fiasco and catastrophe, and before Donald Rumsfeld quit, McCain endorsed George W. Bush against his fellow Vietnam vet, John Kerry in 2004. By that decision, McCain lost any credibility that he can ever put country first. He put party first and his own career first ahead of what he knew was best for the country.
And when the Senate and House voted overwhelmingly to condemn and end the torture regime of Bush and Cheney in 2006, McCain again had a clear choice between good and evil, and chose evil.
He capitulated and enshrined torture as the policy of the United States, by allowing the CIA to use techniques as bad as and worse than the torture inflicted on him in Vietnam. He gave the war criminals in the White House retroactive immunity against the prosecution they so richly deserve. The enormity of this moral betrayal, this betrayal of his country's honor, has yet to sink in. But for my part, it now makes much more sense. He is not the man I thought he was.
The rest is here: http://andrewsullivan.theatlantic.com/the_daily_dish/2008/09/mccains-integri.html
I, too, am disappointed. Of all the GOP candidates I liked John McCain the best. I thought he was a man of honor and I expected, for a change, that we would be treated to an above-board, issues-based campaign between these two men.
Instead we're getting the Rovian politics that have robbed the Republican party of its soul in a Faustian bargain for power. It's evident now that it didn't matter who the GOP picked (with the possible exception of Huckabee), the Republicans no longer even know how to campaign on issues. The Reagan era is dead. Issues no longer matter.
For the good of the party, (not to mention the country) McCain must lose. Perhaps, out of that wreckage someone can rebuild the party based on some authentic conservative values. Maybe it will be Huckabee, with his populist and faith-based but optimistic vision. Maybe it can be Petraeus, who will be a bona fide war hero and is apparently a "Northeastern Republican" (a nearly dead breed, but one that could actually win over independents) in the mold of Eisenhower. Perhaps there is some Obama-like young Republican who can take the party in a new direction.