Being Anabaptist to some extent in my theological understanding makes the consideration of politics a bit more difficult for me (see Bob Robinson's thoughtful, good post related to this, along with my comment). Of course Anabaptists differ among themselves as to what Christians should do related to the state and politics. Some withdraw completely (the Amish and some Mennonites) and others actively engage in it (other Mennonites, Ron Sider among them).
Christians are salt and light in Jesus in this world, and this is to be evident to others. I don't see much in the New Testament which tells us that we're to Christianize government as in trying to see it changed. Yet our influence should be felt everywhere, including government, so that at least the new way of being human in community in Jesus will be evident to them.
Of course in this our lives should be full of good works. And we need to live out and speak the truth which often will contradict the values of society at large, in our case often bent on pursuing "the American dream" and protecting all "individual rights" such as "the right to choose."
Yes, Jesus is Lord; therefore Caesar and any other human government is not. But this was lived out and proclaimed in a way that seems above the world, and in that way to hopefully influence the world. A good case in point in my mind is Martin Luther King, Jr. He refused to live as the world does in protesting against the maltreatment of African-Americans. Instead he sought to follow the way of Jesus in nonviolent protest outside of the system. And that's the major reason we still remember him today.
Of course I think we also need the William Wilberforce's (also here)- to go along with the John Woolman's- working in government. I think a Christian can do that according to their calling, and should. Not an easy road. But think of Daniel and Esther. God will guide one, and we have to decide just how we'll do this in working with others and knowing what we should do. Not an easy calling, but then again what is easy in this life? To follow Jesus in his way will be challenging for us all in whatever way we serve here.
What do you think about this?