The way the article starts it is as though they expected people to be pleased with the President for pushing through and signing into law legislation they strongly and overwhelmingly opposed. Of course his approval has gone down - he is doing things the people clearly don’t approve of - it stands to reason.
I think there was some accepted conventional wisdom that he would be able to convince people to like ObamaCare, once it was forced through. That danger still lurks. People are stupid and gullible (if they weren’t, Obama would not be president and Pelosi would not be Speaker).