Why should he resign? He didn't know about the explicit IMs.
The Dems WANT him to resign, then they will be running around the media outlets trumpeting, "If he wasn't guilty, he wouldn't have resigned!"
Hastert resigning would be STUPID and wrong.
Of course he didn't. After learning of the creepy and inappropriate emails, Hastert did absolutely nothing. How can you expect him to discover the IMs?
Doing nothing about the emails is why Hastert is in trouble with moral values Republicans.