We are assisted by the gifts of the Holy Spirit, aided by the witness or advice of others and guided by the authoritative teaching of the Church. While it is true that a human being must always obey the certain judgment of his conscience, yet it can happen that moral conscience remains in ignorance and makes erroneous judgments about acts to be performed or already committed. This ignorance can often be imputed to personal responsibility. This is the case when a man takes little trouble to find out what is true and good, or when conscience is by degrees almost blinded through the habit of committing sin. In such cases, the person is culpable for the evil he commits.
Voting involves an exercise of moral judgment.
It is a major contemporary fallacy to think that morality has no place in political life. When we vote, we should pursue our deepest convictions concerning the things of greatest importance. Party labels do not absolve us from a profoundly personal exercise of conscience. The imperfection of all human enterprises, including politics, are obvious. Party loyalty is never an excuse for rejecting a moral good.