I'd been trying to promote gun ownership and training among left leaning folks since early 2016. Took various friends and Facebook randoms to the range and taught them to shoot. Have had motivation issues with that project for a while though.
Cheapest option is an assault 12 gauge.
I don't think I've come across any "assault shotguns", but maybe you're referring to the "tactical" variants? They'll typically come in black rather than wooden or camo pattern, have shorter barrels, and hold more ammo when compared with hunting shotguns.
It's important to note that shotguns aren't super beginner friendly, though they're probably the most financially accessible option for home defense. One piece of advice I would give is to look up what "cheek weld" is when using a shotgun (in additional to general safety and usage info). We're also pretty late in the game here for those that are worried about election-related violence, since developing marksmanship skills takes time. Better late than never though, just try to get at least one range trip in so that you can familiarize yourself with the basics.
Not looking to turn this into a guns thread, since that wouldn't be very useful for the OP. If anyone has any questions on the subject, you could make a post in one of these communities, and I (and probably others) can give advice:
It goes both ways, really. You're right in that Trump couldn't have gotten elected without the existence of that reactionary base. That's always existed in American politics, though its strength has varied over time. However, his presence in politics energizes them, and inspires them to organize and spread their propaganda, while also serving as a powerful propaganda mouthpiece himself.
You're also right that Trump's exit from politics won't calm things down right away. Hopefully his movement won't find a new Fuhrer figure, though that's always a possibility.