The official position of the Catholic Church with regard to voting is exactly this: If you vote for a candidate because the candidate is in favor of abortion, then it is a grave sin. If you vote for a candidate IN SPITE OF the fact that they believe in abortion, it is not. It is allowed. Secondly, you have failed to understand that NOT voting for Trump does not automatically mean that the person in question voted Democrat. There are more than two parties in American politics.