The founders of the American republic and their dear Mr. John Locke were quite sanguine with Christianity (specifically non-miraculous Jesusian principles) as their nation's foundation. FDR didn't have to deal with the decay of virtue that modernity ushered in during the latter half of the 20th century. Order and societal cohesion gave way to the language of "rights."
But the Founders wouldn't have been particularly concerned with Rev. Jerry. Falwell's wildest statements were coherent with even theological outliers like Tom Paine and that notorious sybarite Jefferson, both of whom accepted a Providential God (and Who conforms most closely to the Judeo-Christian one above all others), and Who favored the virtuous and allowed the wicked to fall from His favor.
Jefferson himself suspected that the young republic might soon be punished for its toleration of the "peculiar institution." The punishment, if it was such, was grave indeed, today commonly called The Civil War. We can say that even Rev. Falwell's opportunistic/inopportune statement about 9-11 being a result of the United States' fall from virtue isn't terribly out of line with even the most skeptical of the Founders. Go figure.
Jerry Falwell was unsophisticated to be sure, and the moderns will miss kicking him to the curb, since he was pretty easy pickin's. Dear Mr. Locke may not prove to be such a cakewalk, because when one speaks of America, one cannot push him out of the way, one must go through him.
Unless one chooses a path through the gutter, of course. Jerry Falwell would have liked that linked essay, I think, and so, R.I.P. In the end, his public life (not his ministry, which never made the papers) wasn't about Trinitarianism or heaven or hell. It was about virtue.
I'm out on a limb here, but I think even Jefferson would have found some sort of good word to say about him. Certainly George Washington would've:
Of all the dispositions and habits which lead to political prosperity, religion and morality are indispensable supports...[L]et us with caution indulge the supposition that morality can be maintained without religion. Whatever may be conceded to the influence of refined education on minds of peculiar structure, reason and experience both forbid us to expect that national morality can prevail in exclusion of religious principle.---Farewell Address, 1796
The Rev. Falwell has passed from the scene. His Bible, John Locke, George Washington, and Thomas Jefferson have not. The dialogue, and the inquiry, sustain. We cannot relieve man's estate while ignoring his soul.