Former President Bill Clinton displays a great body language cluster of honest regret at the 0:48 mark of this video. It is expressed as several microexpression directed towards Mitt Romney and his director of communications, Eric Fehrnstrom. Mr. Clinton acknowledges that sometimes, one of the worst thinks in politics is to tell the truth - as Mr. Fehrnstrom did when he started the "Etch A Sketch" controversy (see also Secret # 1486: Etch A Sketch, Romney & Eric Fehrnstrom Gaffe).
Note the entire width of Bill's forehead is contracted - simultaneously elevating his eyebrows as well. Mr. Clinton's eyes are opened slightly wider than the resting/relaxed state would dictate. In this context, these all serve as signals of increased emphasis. This is one of the few times when eyelids are opened wider than usual other than when fear, rage or surprise predominate one's emotional tone. This is followed by a brief, but noticeably extended blink - an attempt at blocking or "wiping" the thought from his mind's eye (as if to say, "I'd hate to be running his campaign - because we couldn't fix this problem").
Mr. Clinton's head is also tilted very slightly (usually this component of this cluster is somewhat greater in amplitude). His mouth is highly characteristic of regret - that of tightly stretched lips with a co-existing "inverted smile".
Although the former President is left-handed, his brain is wired much like a right-handed person (thus he probably is ambidextrous). Bill looks down and to his right when he experiencing a strong emotional tone - particularly that involving empathy or sadness (statistically, it would be more common for a left-hander to look down to his/her left when experiencing such emotions).
In a nutshell, Bill Clinton agrees with Eric Fehrnstrom - there will be a "reset" or "shaking of the Etch A Sketch", once the Republican primary is over. However, Clinton does not believe Mitt Romney will be able to pull off any "move to the center" for the November election.
One of the big reasons while so very many people love Bill Clinton, even republicans, is his ability to project empathy and sincerity. It is a fundamental human quality to which of us are naturally attracted. Love him or hate him - few approach his ability to do this. Many would benefit by this skill. What's your "Sincerity Quotient"?