It would be an embarrassment to the Administration if he ran and lost. The press would be relentless about the implications and it could threaten Biden being on the 2012 ticket. Therefore, if the calculation is that he might lose, he will invent some reason not to run.
Kinda like losing the Olympic bid. And this bunch is proud to welcome an ass like Al Franken. Plenty of weasels have lost their first bid for office and gone far.