Thomas Jefferson
Ed Brayton's discussion of the historical validity of claims of Thomas Jefferson's support of a "Christian Nation" is illuminating.
Turns out, it's a myth. A story passed down third-hand to a pair of people who were under 10 years old when it happened (and substantial cause to misremember), and inconsistent with Jefferson's writings and known activities.
Further, the cherry-picking to suggest he attended services in Capitol each Sabbath day is downright hysterical. Read it, it's golden.