Personally, I don't see this guy ever resigning. He's not like Nixon, he has no sense of honor.
Instead, he's got a messiah complex. If you don't believe in him, it's your fault. If the people turn against him, it's their fault. He won't be able to relate to any argument based on party survival. It's his survival that is of the utmost importance.
I can see him just "giving up", however -- when he doesn't get what he wants and he's made a totally unmanageable hash of things. But, still, he wouldn't resign. He'd turn the decisions over to somebody else, continue to enjoy the White House, Air Force One and his other perks.
In any event, we're in a world of hurt...
But hasn’t he been doing that since day one?
Well think of it. 2012 comes and he is losing big in the polls,he feels as if he is going to be unseated. He makes the ultimate sin and brings the USA down by starting a nuclear war with who knows... Then the Mayans were right... OK tin foil hat on.