Guns move easily across state lines, so a patchwork of state regulations doesn’t really solve the problem; if we are to stop the use of assault weapons in mass shootings, we need a national sales ban. That is currently impossible, due to the filibuster. Could a national referendum help?
Yes. While it would be necessary to define “assault weapon,” which is a tricky task, the question itself would be relatively simple, and lends itself to a yes or no answer. That is ideal for a referendum.
The constitutionality of such a ban is currently an open question. It is possible, of course, that Clarence Thomas would flip the bird at the American people and tell them that their opinion doesn’t matter–he only cares about himself and Blackstone. That would require a level of arrogance that even Thomas might not be able to attain, however. It would be worth a try.