Should we still attempt to radicalize these folks when they’re waving American flags and telling people to vote for Democrats?

Yes, because that's where the masses are, whether you like it or not. Idk who else you'd be radicalizing.

“To refuse to work in the reactionary trade unions means leaving the insufficiently developed or backward masses of workers under the influence of the reactionary leaders, the agents of the bourgeoisie, the labor aristocrats, or the 'workers who have become completely bourgeois'" - Vladimir Lenin, Left-Wing Communism, an Infantile Disorder

The organizing conditions of No Kings are more favorable than a reactionary Tsarist trade Union. I think you can handle it.