It is a basic point of the faith that we cannot promote or otherwise endorse evil in order to achieve good. I do not see where voting for Trump is endorsing evil, otoh, it is easy to see that voting for Biden is certain to promote and endorse evil.
Well, when one is voting for Trump, one is voting for some evils that come along with him (that have been adequately docuмented on this thread). So, for instance, one is voting for someone who condones and even glorifies sodomy. At the same time one is voting for someone who has shown some commitment in favor of the unborn. So there's some good, and there's some bad.
But what a Catholic voter does is to promote the good (anti-abortion) while also at the same time recognizing that there's evil that has come along with it. So, for instance, the classic case of double effect is to perform an operation in an ektopic pregnancy to save the mother's life, knowing, however, that it will cost the life of the unborn child. Even such an operation has to be performed very carefully so that one does not directly take the life of the unborn child, but, rather, removes the thread to the mother, without directly causing the death of the unborn child. So the question of double effect with Trump is whether one's vote actually directly causes the evils that might be promoted by Trump during a second term. This is where the application of double effect to voting becomes murky, and this really needs to be developed by Catholic moral theologians. It's an extremely neglected aspect of Catholic moral theology.