Nothing but a violent revolution will actually change anything, but you can still flip the question on electoralism and ask them why they don’t vote for a third party and condemn the country to a two party hellhole. They will still claim that it’s “a vote for Trump” but it might get them to think outside the narrow box that every American is allowed to think inside.
Communists would never be given real power within a system that is built and enforced around the capitalists.
The power the working class has doesn’t need any office or government legitimacy, it exists no matter what. It’s the power of producing everything a society requires to function and massively outnumbering the bourgeoisie. When the working class organises, material conditions are bad enough, and the right opportunity arrives, the working class is unstoppable.