The Sweater Set
That should be the nickname for the duo of Sens. John McCain and Joe Lieberman, the latter of whom (a Democrat) endorsed the former (a Republican) for president today -- in matching sweaters! Generally I think that endorsements do little to win support for a candidate, but this one may be different.
Usually, a high-profile endorsement is treacherous because, for all the people it can woo, it can also alienate others (i.e., Pat Robertson's backing Rudy Giuliani, or Jim Gilchrist's support of Mike Huckabee). But the only people who don't like Lieberman are the hard-core lefties, and they're not going to support a GOP candidate anyway. So a Lieberman endorsement costs McCain exactly zero votes, while possibly making him more attractive to moderate Democrats in the general election, as well as to national-security-first Republicans who might otherwise lean toward Giuliani in the primary.
If nothing else, should McCain win the GOP nomination (doubtful), expect a rockin' Lieberman speech at the GOP convention next summer.
And a prediction: If McCain is president (doubly doubtful) and the Democrats control the Senate by only one vote (triply doubtful), expect to see Lieberman bolt parties and return the Senate to the GOP ...