Julia Shaw has written a nice essay on James Madison, the principle author of the First Amendment to the Constitution....an amendment which some Americans, notably our president, do not seem to think still matter.

"Madison’s original draft of the First Amendment read: “the civil rights of none shall be abridged on account of religious belief or worship… nor shall the full and equal rights of conscience be in any manner, or on any pretext, infringed…” Though somewhat less expansive in its protections, the final version bears Madison’s mark: “Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof.”

"James Madison: Father and Defender of the Constitution" can be found at The Foundry, the The Heritage Foundation blog. I recommend you read it!