The point of communist electoral participation is to agitate. The small chance of winning is only a secondary benefit. By running a campaign Carter can highlight all the ways his establishment competition is unfit to deal with the moment, and if he loses he can demonstrate that bourgeois democracy itself is unfit to deal with the moment. Of course, that's investing a lot of faith in Carter, which is fully debatable.

Whether or not we can win is not the reason we run campaigns. We run campaigns to show that the entire process is a farce. We run campaigns specifically because we cannot win through electoral politics. We do it to hammer the point in to people's heads that better things are possible, but you aren't going to get them by playing this rigged game. This only works if the campaign is being run with that intent though (unlike Bernie, who did everything in his power to reaffirm confidence in the farce of bourgeois democracy and funnel a borderline revolutionary contempt for the system back into the system).

A lot of people may consider this to be a waste of time and effort, but I think as long as you leave the possibility open that "maybe we can make things better if we ran electoral campaigns," it will be a roadblock to radicalization. You need to make it clear that electoralism is not the solution, and the occasional demonstration goes a lot farther in making this obvious to people than reams of theory. You need to foreclose that possibility entirely if you want people to move en masse to the next step.