You know, this already happened in New York city. First they had everyone register the "evil" guns, promising - of course - that the lists would never be for confiscation. Then, some years later they banned all the semi-auto rifles and cops actually went door-to-door making sure all those guns were out of the city.
There is no reason they couldn't try this if they have support in both the House and the Senate.
"In St. Louis, armed Homeland Security agents monitored Tea Party members protesting the IRS. Good idea. When people think their government is out to get them, the best response is to send the government out to get them." -Fred Thompson