Terry v. Ohio (1968) allowed cops to detain on “reasonable suspicion,” which evolved into post-PATRIOT Act terrorist watchlists and the ability to detain on the “suspicion of terrorism” (specifically, the National Defense Authorization Act for Fiscal Year 2012 enables indefinite detention). This expansion of the ability to detain on suspicion was handled and overseen by both the Bush Jr. and Obama presidencies and it’s finally found its natural conclusion under Trump. Likely, Biden will not curtail these expansions.

With Trump declaring Antifa a terrorist org and S.Res.279 (official legislation for declaring Antifa a terrorist org) moving through the Senate, and these protests also being declared Antifa or riots or whatever, the cops have the freedom to arrest whoever they want - a power they always had defacto but now one with official legal backing and zero negative repercussions.

There have been people detained who just live in the neighborhood and were getting groceries during the 2020 uprisings. The “reasonable suspicion” the cops are relying on is merely being near a protest.