What do you mean he is good at "lowering the bar"??
It is something he has discussed himself. Politics is a game of managed expectations. When you set the bar high (John Kerry is a master at this idiocy) and promise to do everything from winning the war in a day to curing Superman, you set the bar so high you are going to fail. Everyone gets mad at you and you loose.
However, if you are quiet and allow the poll numbers to drop, mispronounce nuclear so people think you're an illiterate boob...the expectations are that you are completely incompetent. That allows you to leave people pleasantly surprised and thrilled with your accomplishments.
It basically comes down to a game of never promise too much. Promise little and deliver more. And the President is an absolute genius at this. Breathtakingly good. It is actually a strategy that I have started to use professionally with terrific results.