Huckabee claimed that the majority of the signers of the Declaration were clergymen. This site notes:
Only one of the 56 was an active clergyman, and that was John Witherspoon. Witherspoon was a Presbyterian minister and president of the College of New Jersey (now Princeton University). A few more of the signers were former clergymen, though it's a little unclear just how many. The conservative Heritage Foundation said two other signers were former clergymen. The religion web site Adherents.com said four signers of the declaration were current or former full-time preachers. But everyone agrees only Witherspoon was an active minister when he signed the Declaration of Independence.
The site notes the reason for the confusion:
One issue that may contribute to the confusion about which signers had a history in the clergy is that during the time the Declaration was written, people who studied at universities often received doctorates of divinity, a common degree designation, even if they were not working clergy, said Mary Jenkins of the Independence National Historical Park.
Barton is the one who most notably asserts something along the lines of 27 signers of the Declaration of Independence had "seminary" degrees. The reality is, they had degrees from places like Harvard, Yale, and Princeton which were originally founded with orthodox Christian missions.
Something the Christian Nation crowd doesn't tell us about these "Christian" colleges is during the time the founders (and the ministers they followed) were educated, those colleges became hotbeds of "infidelity" and even the seminary schools trained their ministers in "infidel" principles. The result was Harvard trained ministers like Jonathan Mayhew, Samuel West, and Charles Chauncy embraced theological unitarianism, universalism and rationalism and, in so doing, arguably ceased being "Christian," (or at least "Christian" as defined by its historic orthodoxy). These men also delivered the most notable and influential pro-revolutionary sermons from the pulpit. And even Witherspoon, who was an orthodox Christian, when he argued for Revolution from the pulpit, left his orthodox Christianity at the church door and instead turned to Locke, the Scottish Enlightenment and rationalism, because the Bible/orthodox Christianity could not provide a sufficient basis to justify revolt while those a-biblical sources could and did.