My suggestion if there really is no one and the “lesser evil” is liberals under the discipline of the DNC, then voting in that case is usually just detrimental. The thing to be concerned with in that situation is agitating under a socialist banner, appealing to things like materially improving people’s lives, and while I wouldn’t consider the electoral element to be that important, these things can be a basis for socialist candidates running and trying to appeal to people sick of the GOP and Dems, which more people voting for neither would benefit.

People try to play the “harm reduction” game in various ways and I think we have decades of history demonstrating that that’s a political dead end, and the only way to even potentially get by is by having the courage to start small from an independent socialist banner rather than give the Dems more power while ultimately getting consumed by them. If your only justification is that the liberal will bail a tiny bit of water from a sinking ship, that is inadequate because you are simultaneously feeding into their project of keeping the ship sinking, and I can only really imagine an exception in the case of them being – to a high standard of evidence – both willing and able to advance policy that will directly benefit socialists in a positive sense, not just by being “not the Republican”. An example of this that some Dems do campaign on is ranked choice voting; if you have someone who is credibly dedicated to and credibly capable of establishing that, then I think voting for them is fair.