The Nation asserts:
Bachmann was a research assistant to John Eidsmoe for his 1987 book Christianity and the Constitution: The Faith of our Founding Fathers, in which Eidsmoe wrote “the church and the state have separate spheres of authority, but both derive authority from God. In that sense America, like [Old Testament] Israel, is a theocracy.”Bachmann discusses the influence of Eidsmoe, and faux-historian David Barton in a video to which the article in The Nation links.
"Rewrite, Sugarcoat, Ignore: 8 Ways Conservatives Misremember American History"
A reasonable working hypothesis suggest itself. Michelle Bachmann's history gaffes proceed not from the pressures of the campaign trail, but from faulty training and cultivation of systemic error.