Was america founded as a Christian nation?

Nope. It was founded on political ideas that came from the Enlightenment, which actually broke from Christianity in many ways. Enlightenment thinkers valued reason, provable science, and rationality over faith--these thinkers include Franklin, Adams, Jefferson, and many others of our Founding Fathers! Of course, a lot of these Founding Fathers were Christians as well, but the idea was always that all religions would be welcome, and that Christianity would not be the main one. In fact, the "freedom of religion" part of the Constitution means that Christianity is equal to all other religions in America, and to no religion too. It's fashionable now to think that America was founded on "Christian values," but those same values (equality, freedom, loving your neighbor, etc.) show up in other religions and philosophies just as much as in Christianity.