Conservatives who want to make hay about the religion (or lack thereof) of the President or members of Congress should re-read the Constitution. Toleration of other religions was so important the Founders included it in the original text. Article VI, paragraph 3 says: “…no religious Test shall ever be required as a Qualification to any Office or public Trust under the United States.”
This was a huge step at the time, a deliberate slap in the face of the laws of Great Britain, which barred office holders (and the king!) from being Catholic.
If the Founders intended us to be a Christian nation, they had their chance. They could easily have written a requirement that anyone elected to the government be a Christian, just as they required them to be a certain age, and required the President to have been born a US citizen. The fact that they not only didn’t require it, but specifically forbade any such requirement, means they deliberately built religious toleration into the foundation of the new country.