As I mentioned before, Hillary's refusal to pledge to serve out her next term is the perfect issue for Republicans to set up a narrative describing her as opportunistic. But she's still holding out on the pledge against the wishes of 60 percent of New Yorkers.
So why run again for the Senate? Why set this up? As Chuck Todd argues on National Journal (subscription required), she's definitely running for president. So why run again for the Senate? One reason that Todd's analysis suggests is that lets her raise tons of money even though her race is non-competitive:
The former first lady posted the highest off-year Senate fund-raising total we've ever seen, raising nearly $6 million in the second quarter of 2005. With no major opposition for re-election, the idea of Clinton having somewhere between $30 million and $50 million to transfer to her presidential campaign account in January 2007 (the month she'd likely announce something more formal) is very real.
Thus, we're going to avoid the whole "should she run" debate since, in our minds, it's a moot point -- she's running.
$30+ million would make her a massive frontrunner in the Democratic race. But if the American people see her as opportunistically ducking out on New York, it won't matter in the end. And it's not like she's going to have trouble raising money. So why extract it now under false pretenses?