Unfortunately, today many Catholics have not formed their consciences adequately regarding key moral issues. The result is that their consciences do not "sound off" at appropriate times, including on election day.
A well-formed conscience never will contradict Catholic moral teaching. For that reason, if you are unsure where your conscience is leading you when at the ballot box, place your trust in the unwavering moral teachings of the Church. (The Catechism of the Catholic Church is an excellent source of authentic moral teaching.)