As an American, I'm offended by Christian's trying to claim that this country was founded on their religion or principles. America may be made up of a majority of people calling themselves Christians, but "...though the will of the majority is in all cases to prevail, that will, to be rightful, must be reasonable; that the minority possess their equal rights, which equal laws must protect, and to violate which would be oppression." (Thomas Jefferson, in his First Inaugural Address)

Separation of church and state is in the constitution! It's in the first amendment. It may not contain the phrase "separation of church and state," but it's clear from the founding father's writings that the first amendment is clearly intended to keep separate the church and state. Who would know better than it's author, James Madison:

"Congress should not establish a religion and enforce the legal observation of it by law, nor compel men to worship God in any manner contrary to their conscience, or that one sect might obtain a pre-eminence, or two combined together, and establish a religion to which they would compel others to conform." (James Madison, Annals of Congress, 1789)

"Strongly guarded as is the separation between religion and & Government in the Constitution of the United States the danger of encroachment by Ecclesiastical Bodies, may be illustrated by precedents already furnished in their short history." (James Madison, Detached Memoranda, 1820)

"Every new and successful example, therefore, of a perfect separation between the ecclesiastical and civil matters, is of importance; and I have no doubt that every new example will succeed, as every past one has done, in showing that religion and Government will both exist in greater purity the less they are mixed together." (James Madison, Letter to Edward Livingston, 1822)

The phrase "separation of church and state" was first used by Thomas Jefferson in 1802, in a letter to the Danbury Baptists: "Believing that religion is a matter which lies solely between man and his God, that he owes account to none other for his faith or his worship, that the legitimate powers of government reach actions only, and not opinions, I contemplate with sovereign reverence that act of the whole American people which declared that their Legislature should "make no law respecting an establishment of religion, or prohibiting the free exercise thereof," thus building a wall of separation between Church and State."

Jefferson used the phrase again to a letter written to the Virginia Baptists in 1808: "Because religious belief, or non-belief, is such an important part of every person's life, freedom of religion affects every individual. State churches that use government power to support themselves and force their views on persons of other faiths undermine all our civil rights. Moreover, state support of the church tends to make the clergy unresponsive to the people and leads to corruption within religion. Erecting the "wall of separation between church and state," therefore, is absolutely essential in a free society."