Rich Lowry wonders:
She's preparing the demographic ground for McCain, by getting white working-class Democrats used to (if you will) not voting for Obama. And she's softening Obama up for McCain, prodding at and exposing her fellow Democrats' weaknesses.
The following is predicated on the assumptions (for which I think that there's a ton of evidence) that: a) Hillary! is all about power for Hillary! and b) the fortunes of the Democrat Party come a distant second to that.
If Obama wins the election, even if his presidency is disastrous, it makes it very tough for her to run again in four years. Ted Kennedy tried it against Jimmy Carter, and it badly damaged the party in the 1980 election. And Hillary has nowhere near the reserve of goodwill among party regulars that Ted Kennedy does, so if she is perceived to be damaging the prospects for a reelection of a Democrat, it could be the end for her.
But when Obama loses (and particularly if he loses McGovern style, which is not at all unlikely), she'll be able to say "I told you so," and she'll be positioned for another run at the nomination in 2012 (she'll only be sixty four).
Thus, based on the above logic, Hillary!'s preferences are, in this order: a) to win the nomination, b) for McCain to win the election and c) for Obama to win the election.
So what she has to do (on the assumption that Obama is going to be the nominee) is to help McCain win without it being obvious that she's doing so. Fortunately for her, the same things that she has to do to continue to fight for the nomination, all the way to the convention, are the things that will continue to strengthen McCain, and weaken Obama in the general. So she can maintain plausible deniability. And after the convention, most of the damage will have been done, so she can go through the motions of supporting Obama.
And if by some miracle, the stalking horse learns to sing, and she gets the nomination? Like what happens if she loses Super Tuesday, she'll worry about that when it happens.
OTOH, given how close the Democrat primary election is, it is premature to expect Clinton to bow out.
She cant let Obama win the Presidency. it kills her chances in 2012 and beyond.