It's a liberal voter delusion that the 2% of US guns in the hands of the military and police can be used to take away the 98% of guns owned by people who want to keep them. And it is a voter delusion, because the Democratic party wouldn't even be able to get the votes within its own party if there were a chance in hell of it passing, and they know it. It's just a wedge issue. It's effective because the upper-middle class liberal base can imagine themselves being affected by a mass shooting, so they care about it.
Mass shootings are a media boon, because they know that they don't have to do any work for the next week, just dust off all of the timeless partisan nonsense that they published during the last one. Right now a bunch of right-wing outlets are doing the same thing, and gun sales are about to go up.