That's not what he said. He actually said we were a nation of many different religions, including Islam, Judaism, Christianity, Buddhism, and many others including no religion.
We have always been based and were founded due to the Freedom of Religion, not because of Religion. The so called Founding Fathers, and Mothers, came here trying to get away from oppressive religious restrictions and settled here with the freedom to seek the way to the God of their choice, not the God of the King of England.
Here is a blog posting I found this morning that shows the history of this far better than I could ever say it. It is by Eric Grant and he does an excellent job laying it out.
America Has Never Been a Christian Nation
Newt Gingrich, Rush Limbaugh and Randall Terry would all like you to believe the United States was founded as, and continues to be, a Christian nation. They would like you to believe the rights we enjoy as Americans were granted by their god and only their god. These radical neoconservatives forget that freedom from religious oppression is one of the founding principles which led to the formation of the United States of America. And there are a few key moments in history they would rather you forget:
In 1657 a group of early Americans signed a petition requesting the lifting of a ban on Quaker worship. The Flushing Remonstrance, as it is known, was the basis for the Constitution’s provision on freedom from religion in the Bill of Rights.
In 1788, James Madison writes in Federalist No. 51: “In a free government, the security for civil rights must be the same as for religious rights.”
Article Six of the Constitution states that “no religious Test shall ever be required as a Qualification to any Office or public Trust under the United States.”
The First Amenedment to the Constitution states: “Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof;”
The Treaty of Tripoli, ratified by the Senate and signed by President John Adams in 1797, states in Article 11: “…the Government of the United States of America is not, in any sense, founded on the Christian religion;”
The doctrine of separation of church state, which can be attributed to Thomas Jefferson in a letter to the Danbury Baptists in 1802, has been cited by the U.S. Supreme Court numerous times in favor of this principle.
Those radical conservatives who follow a “you’re with us or against us” mentality are no different than those radical Islamists who flew jets into buildings and murdered 2,974 people on September 11, 2001. Those same so-called patriots who claim to cherish the Constitution and our founding principles are the same ones who want to destroy everything America stands for: freedom, diversity and equality under the law. If the folks who worship Fox News had their way, we’d be living in the dark ages and reduced to nothing more than mindless subjects of a Christian theocracy. Thankfully a renewed sense of real patriotism in America will prevent that nightmare from becoming reality.
As you see, he has a great post about it. Again, America was founded on the principle of Freedom FROM Religion, not on the Christianity of Newt, Sarah, Huckabee, Reagan or anyone else who tries to tell us how to believe or what to believe.
The Religious Right would like to make people think they have the privilege to run the country as they see fit. I beg to differ, and History, when you know it, backs me up, not them.