Voting is a prudential issue, which means those in charge of the decision need to be the ones to make the decision, using their knowledge and praying for God’s grace.
There will never be a perfect politician; we can see that through history! Even saints can make mistakes, if only through lack of knowledge.
So we need to consider our Faith, and weigh the issues, and decide ourselves. As an act, we should try to disengage ourselves from considerations of human respect so that we can make the decision freely.
(What Pope Benedict wrote about abortion is that it would be wrong to vote for a pro-abortion politician *because of *his or her advocacy of abortion. But to vote for that person despite the advocacy, *if done for a proportionate reason, *is not.)