Even if you believe that a two party system is the only possibility, you can do many things that don’t involve voting for Trump.

“Useful idiot” is a term coined back in the day to describe people who unwittingly spread the propaganda of communists without really understanding the ultimate goals. In this case being a progressive while disagreeing with the leading ideas of the movement.

And no it doesn’t mean a vote for Trump. It means not supporting candidates that parrot this type of rhetoric and to not support causes/movements that are a part of it. FWIW Trump did ban critical race theory from being brought into federal offices and Biden quickly reinstated it under the guise of “learning to be nice to each other” - which it isn’t. Biden, in this case, I believe is a useful idiot for propagating their propaganda, mistaking it for harmless “diversity training”. There’s a big difference!