Jesus said to render to Caesar what is Caesar’s. Everything is God’s, so Caesar has nothing. Jesus rendered nothing to him, except for surrendering to the brutal power of his soldiers.
A Christian cannot be a democrat or a republican, because they owe their allegiance to Jesus.
Christians cannot give their allegiance to a political government, whether it is democrat or republican, because it is an alternative king.
Christians must give full allegiance to Jesus and his Kingdom, so they cannot give their allegiance to any other king.
Christians cannot be willing citizens of a nation state, because the nation state is an alternative kingdom.