1) You do not have to vote. Despite what people say, you can express your political opinion by not voting. You can be a good citizen and not be a voting one. Not voting says, "Something's rigged; the candidates are unfit; I refuse to believe our voting and governmental systems are right." Personally, I will vote, but it is not a requirement (Christian and or otherwise).
2) This election is not make or break. The pundits warn the end of America as we know it if either major party candidate is elected. The reality is our world will change minimally based on the president, Senators, and the like (the world is already fallen, is is not?). Yes, leaders influence, and yes, policies matter. But the sum and substance of history flows through the human heart. 1930s Germany became what it did not because of Adolph Hitler, but because of the hearts of post-WWI Germans crying out for power and vengeance. It's easy to point the finger at party leaders and political heroes/villains, but culture is shaped by individuals. Change the heart, change the world. Each election is simply a reflection of the culmination of individual values; lament that before you lament and lampoon any particular candidate. Vote your conscience, but more importantly, check your conscience. Do you know what is good? Are you living a good life? How you assess the condition of your own soul is make or break. Are you ready to meet your Maker?
3) The world will not be transformed by political power (good thoughts on this in J.D. Hunter's To Change the World). Whether we vote left or right, we trust in the coercive power of law to make the world aright. The right wants laws to protect the unborn. The left want laws to force others to finance certain programs. And yet, history has shown that coercive power offers little for substantive change. Love changes the world--love marked by service, sacrifice, persuasion, and mercy (cf. 1 Corinthians 13 and Christ's example in 1 John 3-4). Abraham Lincoln won over our nation not by winning the Civil War, but by passing on his conviction of one nation, under God. Martin Luther King, Jr., transformed people through his words, life, and martyrdom. William Wilberforce's success in Parliament fell on the heels of cultural transformation through evangelical preaching and anti-slavery teaching (both amid great suffering and persecution). The coercive power of the state cannot transform the culture. Love (or hate) does.