R.C. Sproul provides some very helpful insights on our responsibility to vote.  I strongly encourage you to read the entire essay posted at the Ligonier Ministries blog that you can access HERE.  Here are some excerpts:

But here is what I’m going to tell you to do when you vote. As a Christian you have obligations imposed upon your conscious that in some sense other people don’t have, although they should have. And the first thing is this: You have to understand what a vote is. The word vote comes from the Latin votum, which means ‘will’ or choice. And when you go to the ballot box and you vote, you are not there to vote for what’s going to benefit you necessarily. Your vote is not a license to impose your selfish desires upon the rest of the country. You only have the right to vote for what is right. And not only do you have the right to vote for what is right, but when you vote you have the duty to vote for what is right.

Sproul also has this to say that I want to endorse:

I know that abortion is not the number one issue in this campaign because it has become acceptable. Just like slavery became acceptable. But it cannot be acceptable to ethical people. The people of God have to rise up and say ‘NO’! We are not asking the state to be the church but we must say to the state, “Please be the state. God ordained you to protect, maintain, and preserve the sanctity of life, and you are not doing it.” So that has to be on your mind when you walk into that voting booth.