Ok, worst case. @02Talon, @th3v0t4ry, @grayzonewarlord, and @KurtSchlichter do this way better than I do.
But, this is twooter, where I can yell my opinions into the void if I want.

Assume that some form of confiscatory gun control is enacted, whether through legislation or EOs and the regulatory state.
Assume further that the feds go all in on aggressive enforcement.
Assume the pressure from the bubble is enough to encourage them to ignore court orders.

Naturally it's challenged in court and red state AGs are suing.
But the media drumbeat says anyone objecting is a white supremacist insurrectionist who probably kicks puppies.
So the state is emboldened to ignore the legal process and forge ahead with enforcement.

Blue states cheerfully jump on board, of course. So do blue city PDs.
Sanctuary states and counties spring up everywhere, and naturally that's NOT OK if they're defending American's rights instead of cartel members.

Now you just need a flashpoint.
It won't be a blue city, because the PDs there will at least on paper be on board, and they're bleeding good cops anyway. So they're left with the douchebags who get a kick from exercising power.
Plus the target demo is scarce there and wants out.

Probably won't be a red state, either. Even a blue PD in Idaho eager to cooperate with the feds is gonna be hemmed in by the state, and it's easy to imagine every red state immediately banning any form of cooperation in enforcement.

That leaves red counties in blue states, or maybe border counties in red states whose closest feds are in a blue state.
Say, parts of northern Idaho close to Spokane?

Assume there's a buildup of enforcement actions that are ignored by media but make the rounds quickly in red circles.
Few if any people are gonna actually go down in a bed of brass when the ATF gets the drop on them. But everyone facing 100 years for mags is gonna mobilize folks

So people start organizing to keep a watch on the feds.
Local cops feed what they hear to friends, and everyone is paranoid.
Every USG license plate driving around a rural area is getting scrutinized.
Someone gets lippy, and naturally ATF shoots his dog.

Now all it takes is ONE enforcement action happening at a time and place where people feel confident enough to resist.
Maybe one where the local sherrif shows up to prevent the feds from acting.
Or just dude has enough fed up buddies to go full Cliven Bundy.

Now you've got two groups facing off with guns, feeling threatened.
Feds feel like they're enforcing the law and these dudes are all criminals.
SD/normal people feel like this is an unacceptable and illegitimate action, and have no obligation to comply with tyranny.

Smart feds at this point back off, but it doesnt get to this point at all if they're smart.
Maybe this happens once or twice and gets deescalated, but 100% if that happens the feds pursue charges.
So the next is less likely to be talked down.
At some point, someone is stupid.

Great, now we have the normie sherrif dept, with a smattering of deputized goons, in a fucking gunfight with feds and whatever local backup is willing to help them.
Like, say, state patrol if we're in a blue state, red county.
All live streamed, because of course it is.

Maybe the feds saw someone with a phone and started shooting.
Or maybe good ol' boy got sick of waiting and thought a .308 through the windshield would get the feds to back off.
It. Doesn't. Matter.
The narrative is set, and even if you wanted to stay out of it, you can't.

The specific shots that best support the narrative of Racist Insurrection to Overthrow Democracy play on repeat on all the networks while they demand Biden or Harris invoke the insurrection act and Do Something.
Meanwhile the right is circulating the exact opposite.

In this worst case, no one backs down (to be clear, the feds should and should never have tried for such an egregious power grab).
One red state decides to evict the ATF in response, then others jump on board.
More importantly, millions of people are activated.

All of a sudden it's not safe to drive anything with USG license plates in HUGE swaths of the country.
Feds from all agencies start reporting broken windows, slashed or shot out tires, and sugar in the gas tank whenever they leave blue areas.

Everyone who gets shot by the feds instantly becomes a martyr, regardless of circumstances. Say their name rallies pop up in red areas.
When the feds try to move on visible leaders, they find them impossible to find or surrounded by allies perfectly willing to fight.

Meanwhile every bit of footage is being used to drive the narrative that resistance to the feds is racism and white supremacy and probably transphobic or something, which further alienates half the country.

And there are shitheads on the right, too. As things devolve someone is gonna get the bright idea to track down a fed or a prosecutor at home. Or to threaten their family.
Or to grab their local informant (probably named Karen) and leave her hanging from a lamp post.

THAT is how a stupid, immoral, and unconstitutional policy detonates a fault like and collapses society.