Not entrapment, just good old opposition research wedded to the politics of personal destruction.
How did any of that make him cheat on his wife and family?
to me it doesent matter; the fact is he committed the act(s). It seems to me if the dems were behind this they would have waited a year or 2 during the hot political seasons. My guess is his lover was going to out the affair so he did the standard confession.
Frankly, I don't even think this qualifies as "opposition research" of any kind. The guy is a sitting governor, and he ran off, unannounced, to another country, to have an affair. If the media wasn't trying to track down sitting governors who leave the state (and the country) unannounced and without telling anyone where he is going or when he will be back, that would be a problem, regardless of which party the governor belonged to.
As bad as Obama has been, and as much as the media has effectively been an extension of his campaign (and now, as President, his perpetual campaign), I don't think this story has anything to do with any of that.