The brazen appearance of white supremacist groups in Nashville left the city grappling with how to confront hateful speech without violating First Amendment protections.
The inside-the-law approach that works to some limited extent is public community rejection. Things like large groups showing up and standing with their back to the Nazis.
Do what punks did to keep them out of the punk scene. Make them feel afraid to show up. You do this by beating the shit out of every single one of them every time they show up or open their mouths.
Loudly ask why mass shootings happen to decent people instead of these scum. Play videos of the bombing of Dresden and the executions after the Nurnburg trials to remind them about what we do to Nazi fuckheads.
Let them march. A bigger problem is that a huge number of people seem to think they're a thing of the past and don't really exist in any strength. Let them prove otherwise.
You can't suppress them into defeat anyway, we've tried that before.
We can't suppress them into defeat!? What?? That's how the German Nazis were defeated! That's how modern Nazis have been symbolically defeated, worldwide. Repeat after me: "We don't serve you here."
Any place, anywhere in the world, if an equal number of people stand up against them and for human equality, they run away with their tails between their legs. They're fucking Nazis...
There were several laws put in place in postwar Germany that specifically suppressed them. This was broadly effective, though I think the modern-day position of the AfD shows it was not completely so.
In the US, any such legislation would be struck down in court as unconstitutional.
Actually, Ulysses S Grant clamped down very brutally on groups like the KKK during the Reconstruction Era, essentially continuing the civil war against the south in a sense. He ended up reducing their strength significantly and driving them underground.
Unfortunately, an idea cannot be destroyed with military might, it can only be fought by teaching critical thinking skills and sound information gathering and decision-making methods, so people don't think so stupidly.