Mass Shootings, Starring white People

1, 2 and 4 are all pretty simple I think.  Red Flag Laws have already passed muster on the state level and have been passed in red states.  The background checks are already passing through a national database, that is easy enough to flag.  And limits on certain functionalities of guns doesn't abridge the actual right to ownership of the guns.

Background checks of all sales is tough because it requires people to meet up at a licensed dealer (we have 4 times as many in the US as we have McDonalds though, so not too tough) or you'd have to have a national database that the public which would likely lead to more gun thefts (see below)

the last one is big to me for common street crime but there are plenty of reasons that people don't report crime to police (being involved in other crimes being an obvious one).