The text of the U.S. Constitution makes no mention of God, Jesus Christ, or Christianity.
"The United States of America should have a foundation free from the influence of clergy."
- George Washington
“The Government of the United States of America is not, in any sense, founded on the Christian religion.”
- Vice-President John Adams, "The 1796 Treaty of Tripoli"
"This would be the best of all possible worlds, if there were no religion in it."
- John Adams
"The purpose of separation of church and state is to keep forever from these shores the ceaseless strife that has soaked the soil of Europe with blood for centuries."
- James Madison
"The Bible: a history of wickedness that has served to corrupt and brutalise mankind."
- Thomas Paine
"Christianity neither is, nor ever was a part of the common law."
- Thomas Jefferson
"Lighthouses are more helpful than churches."
- Benjamin Franklin
"I distrust those people who know so well what God wants them to do, because I notice it always coincides with their own desires."
- Susan B. Anthony
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While many of the Founding Fathers were Christians, some of the most prominent members were Deists and/or very much opposed to any form of organized religion.
If the OP is arguing that Hillary Clinton should be disqualified from holding the office of the Presidency based on what he perceives to be as a lack of a Christian affiliation, the same argument could have also been made to disqualify Presidents George Washington, John Adams, Thomas Jefferson and James Madison.
https://www.azquotes.com/quotes/topics/founding-fathers-anti-religion.html
http://www.adherents.com/gov/Founding_Fathers_Religion.html#Declaration