One idea I’ve wanted to push for some time is to get rid of plurality voting and replace it with a system in which all voters rate all candidates on the ballot. Doing so would make it easier for voters to do what you ask. Let’s say that you’re a hard-core Democrat and that there is no way that you are going to give your favorite Democrat a rating that is less than any Republican, even for a Trump-crossing Republican. That’s fine, even if you were to do so, you would still be able to give a rating to the Trump-crossing Republican and to the horde of Trump-backing Republicans and thus show that you prefer the Trump-crosser over the Trump-supporters. That will not happen as long as plurality voting is in place.