They have long been supported by opponents of gun restrictions, including the National Rifle Association. Yet gun-controllers are whooping it up in the media because recent data indicate that background checks have worked and this is supposed to show that the Brady bill as a whole is a good thing. Professor Lott's statistical data indicate that waiting periods cost lives, rather than save lives. Liberals often assume that other people are irrational, so the idea behind a 15-day waiting period is that these irrational people should not be able to get their hands on a gun when they are angry and might do something they will regret. But there are also quite rational reasons for wanting a gun, including a realization that you are in danger.
Criminals are also quite rational.
So it is hardly surprising that a spread of handguns among the citizenry has been accompanied by both a decline in violent crimes and a rise in non-violent crimes. Since criminals are in the business of committing crimes, they adjust to changed conditions by changing their crimes. Armed robbery is not nearly as much fun when the other guy is also armed. Shoplifting or stealing parked cars may look like a better alternative to getting shot. Some criminals may decide that even an honest job has possibilities.