Why it won't work to appeal to historical documents

An excellent article from the Cardozo Law Review (the law school of Yeshiva University) UNDERSTANDING THE “CHRISTIAN NATION” MYTH   by Steven K. Green, explains why appealing to historical documents will not settle the debate between the followers of David Barton and Mark Noll. Kinda reminds me of how appealing to scripture doesn't settle the debate between Catholics and Protestants.

"The idea of America’s Christian founding persists because
it is one of our chief founding myths. It declares that we are a
special people and nation, that we have received God’s
blessings but are also subject to his judgment when we fail in
our endeavors. It sanctifies our origins, informs our national
identity, and reminds us of our responsibilities. It is a
powerful narrative, and it is particularly appealing to people
who desire a greater religious presence in the public life of our
nation. The myth also persists because it is sufficiently
indefinite in its detail and finds plausible, though not
convincing, support in the historical record. That is why this
debate is unwinnable on a level that simply compares
contrasting historical texts. The religious discourse of the
founding period needs to be examined in its larger context,
including an appreciation of the purposefulness behind the
creation of the Christian nation myth."