Both the Christian Right and the Christian Left get the question of Christianity and politics wrong.
Christianity is not politically conservative or politically liberal — though Christians may be either. Christianity is not political at all. It is in a sense politically agnostic. But in another sense it calls into question the basis of every earthly power, including politics.
Those looking to dig into the Bible and find a political platform are going to be sorely disappointed. It’s not there. That is for the simple reason that it is not a book about politics, but about God, and how He is saving His people through Jesus Christ. This distinguishes Christianity from Old Testament Judaism and modern day Islam, both of which contain detailed political agendas. Well-meaning Christians that want to outline a detailed “Christian” agenda of their own, however, will simply not find one.
When opponents tried to trap Jesus between his fidelity to oppressed Israel or oppressor Rome, he asked whose picture was on the coin, and taught us to render unto Caesar what belongs to Caesar (Matt 22:15-22). When on trial before Caesar, he admitted to being the King of the Jews, but in the same breath asserted “My kingdom is not of this world” (John 18:33-37).
Jesus’s followers likewise taught us to be strangers and pilgrims in the world, subject to the governing authorities. Peter writes, “Be subject for the Lord’s sake to every human institution, whether it be to the emperor as supreme, or to governors as sent by him to punish those who do evil… for this is the will of God” (1 Pet 2:13-14). Paul likewise told Christians living in Rome (under Nero!) that the governing authorities were appointed by God, and they should be subject to them. The only exception is when the state tries to force you to actively violate God’s law (and no, taxpayer funding for abortion doesn’t seem to qualify).
Note that for both Peter and Paul it is God who is ruling the world through the state — though he’s not trying to save any souls through these means, and the Bible isn’t the constitution. He’s just keeping the bad guys at bay, using the light of nature common to Christians and non-Christians. This is good and honorable work, and the New Testament never tells converts to quit their service as soldiers or servants of the state.
Thus the Christian faith represents a radical break from the theocracy of Israel, but Christianity is not therefore inconsistent with the Old Testament. Rather, the model for Jesus’s politics is not Moses, but Abraham, who lived “as in a foreign land” while looking forward to a heavenly “city that has foundations” (Hebrews 11:9-10).
This teaching was political in a narrow sense, insofar as it was extremely threatening to Jewish political leaders and revolutionary zealots who hoped to restore their independence. Jesus didn’t give comfort to any of the political parties of his day, either the conservatives or the radicals (cf., “Life of Brian”). And he threatened Rome as well, by failing to ascribe to it the ultimate status it sought. If he was the King of the Jews, he must be their enemy.
Yet he was a King — the King of Kings — and a radical, in the sense that he proclaimed his coming Kingdom as ultimate and victorious over all earthly kings and kingdoms. The Kingdom of God, however, would not be built or established by any followers here on earth. “If my kingdom were of this world, my servants would be fighting,” Jesus told Pilate, but it is not.