It's been a lot longer than 20 years. The AR-15, for example, was first sold in the civilian market 50 years ago.
This also came just after the peak in basically every category of crimes in 1992. There was a lot more public demand for some kind of action. It still barely passed, which is appropriate considering the fact that it didn't really address the real issues.
In the last twenty years, though, pretty much all types of crime are down 40-60%. So the political climate is somewhat different, or it would be if the various media and the Obama Administration weren't riding the immediate emotional climate for all that it's worth.