This is expected. Obama and his allies rammed Obamacare through by devious means; he has routinely exceeded his authority and made numerous recess appointments, when the Senate was not in recess in order to sidestep troublesome confirmation hearings; gutted the work requirement from the 1994 welfare reform law, in spite of both constitutional limits on the power of his office, and of clear and unambiguous text in the law specifically prohibiting this very thing; and decided to selectively enforce immigration laws to achieve the effects of the "dream act" when he and his party couldn't get it through congress. Was there ever any doubt he'd exceed his authority in the same way over the issue of gun control?
It's probably going to take a legal challenge to whatever executive orders he issues, and get the supreme court to rule it unconstitutional. And at that, we'd better get that accomplished before Scalia, Alito, Thomas, Roberts, or even Kennedy dies or retires and Obama can appoint a replacement, who will unquestionably be very liberal. If that happens before the issue comes up, we're sunk.