Looks like McCain's signaling his intentions:
Of course, Mr. McCain said, President Bush's nominee will be a conservative. "He campaigned for re-election and made no bones about the fact that it would be a conservative nominee," Mr. McCain said. "Elections have consequences."
Indeed they do. More to the point, upcoming elections have consequences. And let's not forget how McCain's principles worked in 2000 (from the May 30th New Yorker):
McCain beat George W. Bush in New Hampshire, in a nineteen-point upset, but the storybook campaign ended when the Bush machine retaliated, in the infamous South Carolina primary. McCain had hoped that South Carolina's large veteran population would help him win there; but the Christian Coalition, deeply entrenched in the state, became the decisive constituency. Somewhat surprisingly, McCain had the support of Gary Bauer, the social conservative, who had dropped out of the race by that time. "I wanted a commitment from either George Bush or John McCain that if elected he would appoint pro-life judges to the Supreme Court," Bauer told me. "Bush said he had no litmus test, and his judges would be strict constructionists. But McCain, in private, assured me he would appoint pro-life judges."
McCain wants to be President. And he sure as hell won't be if he fights the base on the Supreme Court.. Looks like we'll be looking elsewhere for allies.