“Dealbreakers”

I can’t recall when or where, but I believe it was hilzoy who gave the best answer I’ve ever heard to this kind of question, which I wholeheartedly endorse. It was, essentially, that she would be indifferent to voting for the least bad viable candidate when things had gotten so bad that she was actively involved in violent rebellion against the government. Significantly, this is a higher threshold than “things are so bad violent revolution is justified in the abstract, but I’m not currently doing it”, but actual active rebellion. This seems exactly right to me. Either you should use the tools available to make better/reduce the harm of the current state, of you should begin engaging in a plot to overthrow it, or find a way to contribute to an ongoing one. If the latter is not to your taste because you have other priorities, or you (probably wisely) deem it unlikely to be unsuccessful and as such not a reasonable risk of life and limb, you have no reason to avoid the first strategy, and you get no credit for moral high ground for avoiding it.