My friend Chris recently wrote this post on this subject, and I believe he expressed himself very well. I also completely agree with him. My faith forms the very basics of my ethics and morality. I can I ignore such things like my morality when voting for persons who are going to influence not only my life, but every person around me?
My last post was dealing with my view of war and killing, and how it differed between the Church and the government. Many people saw this as a contradiction, and one person noticed a similarity with Martin Luther's theology of Two Kingdoms.
However, I don't think that my view is really that official. The Church is an ideological institution. It's design and purpose is to house, educate, and equip God's people as they represent Him in the world and spread His Kingdom and influence through the love of Christ. The government is a pragmatic institution. It's design is to protect people from threats foreign and abroad, and to develop an social infrastructure (i.e. common currency, roads, etc) to enable society to function. Violence is never a good thing, but it is sometimes very practical and necessary.
As a Christian, when I vote and consider public policy, I am weighing out two things: morality and practicality. I don't expect the government to be able to defend people without being violent (even though appeasement strategies worked so well in the 1930s). I also don't expect there to be a law against every sin in the Book (laws are meaningless if they can't be enforced, and immoral if they can't be enforced morally).
These are things that have to remain in tension, not because it is some grand mystery on how they work, but because how that tension plays out may vary from situation to situation.