Here is another great Michael Horton quote from the CRI article on authoritarianism:
Scripture admonishes us, [with Christ’s words ‘my kingdom is from another place’] to avoid either the tendency to confuse the kingdom of God with an earthly nation (Israel, America, etc.) or, on the other hand, to view citizenship in one kingdom as completely antithetical to citizenship and participation in the other. (p. 5)
I cannot overemphasis the necessity of this Protestant two-kingdoms approach. Separation of church and state is actually a good thing.