I'm not as familiar with Peter Leithart as I probably should be. He is a Presbyterian theologian. I seem to recall that he was embroiled in the "federal vision" controversy.
Regardless, Leithart recently gave an interview at the Gospel Coalition. These remarks I found particularly relevant against the backdrop of the heat and froth of the party conventions, especially where "God" and "Jerusalem" language is being batted around:
Americanism has a way of reading the Bible (with America sometimes playing a prominent role in the biblical story as the “new Israel”), an eschatology (America is the “new order of the ages” and the “last best hope of mankind”), a doctrine of political salvation (everyone becomes like us, and all will be well), and, since the civil war, a view of sacrifice (American soldiers give their lives, and take the lives of enemies, to make the world peaceful and free).
For many American Christians, American exceptionalism involves some degree of adherence to Americanism. Americanism is a heresy; in certain respects it is simply idolatrous. Jesus, not James Madison, brought in the “new order of the ages.”
The practical effect of Americanism is that it blinds Christians to the real evils that America has perpetrated and also obscures the central importance of the church as God’s empire on earth. Americanism encourages Christians to support the American cause no matter what, because the future of the world depends on America. Even when we’re bombing civilians or sending billions of dollars in military aid to Muslim dictators, Christians still wave the flag and sing America’s praises. And for some Christians, criticism of America is almost tantamount to apostasy.
...teaching the Bible means teaching Christians that they are Christians first before they are Americans; it means teaching them that their Christian brothers in Iran and Iraq are closer “kin” than American unbelievers. Teaching the Bible means attacking the idolatries associated with Americanism. Teaching the Bible means teaching people not to kill, even if the American government says it’s OK.
Another obvious thing is to cultivate the communal life of the church, and that means putting the Lord’s Supper at the center of Christian worship. The Supper is where we who partake of one loaf are made into one body; by participation in the Supper, we are formed into God’s rival empire.