Suzanne, If we're going to talk about two evils, maybe we should talk about the third, which would be to have a power vacuum and chaos or a dictatorship. We will not have a perfect candidate, nor a perfect bishop, or parent or child or friend ...
The freedom to act in the polis was invented by the Greeks and was a wonderful and providential preparation to the Gospel freedom as understood by the early Christians and those who followed in many different societies and political systems. The first Christians brought freedom to a new level when they lived the experience that it is better to fear those who kill the soul than those who kill the body. They lived the truth supremely in their bodies in martyrdom and some today still do.
In the amazing book by Hugo Rahner, Church and State in Early Christianity (it's out of print, but everybody should find and own a copy and keep it), these persecuted Christians made a point of being good citizens and praying for the emperor. This call for prayer was insistent and taken seriously. Even if voting wasn't an option, they lived very much at the center of things and interested in it all. I don't think we are called to stand to the side of things; otherwise, we live a dualism (or alternate ghetto culture) which wasn't the case with the early Christians. Things only changed because they were involved, and in particular the popes were vocal with the emperors. It is documented that these early popes were the voice of freedom in the world, which is first of all the freedom to believe in and worship God truly.
The freedom of the person (which truly is not expressed in having an abortion or by committing any other inhuman act) affirms that "Every hair on your head has been counted." It means that the smallest and weakest among us matters, because each is loved by God. Democracy is an affirmation of this value of the person, however flawed it may be in practice. Obviously a secular society does not recognize the foundation of the freedom of the person, created and destined by God, and this is the reason the protection of the human is eroding and so much at risk.
We don't have to win an election, but we do have to bear witness as the Pope does continually in his statements to world leaders. Maybe it's good that we have to offer a nuanced participation in an election, because we have to recognize the Republican (or Democratic) party is not going to save the world.