Why won't weiner resign?

It seems that Wiener has screwed his whole party, and brought negative media attention to himself at a time when democrats would rather stay out of the spotlight, yet he stands erect, declaring that he will not pull out. Why would Weiner do such a thing? After Obama killed Osama Bin Laden, dems had such a good position from a PR perspective, and then Weiner pops out and does this? I think its a shame.