Liberalism (I don't mean that as in 'left wing' or 'progressive', I mean it as in 'the Enlightenment political ideologies about liberty which the USA was founded upon') is founded on ideals like free speech and political association. They won't be prosecuted in the USA for being Nazis, they're constitutionally protected. Institutions will protect their ability to do this.
It allows us to identify them, but justice will not be delivered by the institutions here. That's where the community must come in and act, legally or otherwise. They can't offload their responsibility onto police this time. The community must organize and defend itself against fascists. Them being out and about just means we haven't made them scared and hurt.