He ran for president before... I believe his run was derailed for plagiarizing.
He volunteered to be McCain's running mate... and then accepted the position for Obama.
Immediately after he became Obama's running mate he began attacking McCain. That kinda put a bit of a strain on his credibility.

The media attacked McCain through his running mate Sarah Palin, highlighting and spotlighting her flaws but oddly enough failed to do the same with Biden.

Biden is an incredibly flawed candidate... he's a master of gaffes, a plagiarizer, a panderer, and as a policy maker an utter and abject failure.
Despite all of this... if the touchy creepy thing is what it takes to disqualify Obama's Right-handsy Man... I'm okay with that.