It is the church's job, as Dr.[Martin Luther] King says, to be the conscience of the state, not the chaplain of the state.
God can use anything, and anyone - even a king or a president, even a tax collector or a businessman, a priest or a prostitute, a Republican or a Democrat.
In the Bible, God uses brothel owners, pagan kings, murderers and mercenaries as instruments of good; at one point God even speaks to a guy named Balaam through his donkey.
This is what Jesus had in mind: folks coming together, forming close-knit communities and meeting each other's needs-- no kings, no major welfare systems, no presidents necessary. His is a theology and practice for the people of God, not a set of suggestions for empire.
...I believe in a God of scandalous grace. I have pledged allegiance to a King who loved evildoers so much he died for them, teaching us that there is something worth dying for but nothing worth killing for.