--Article 11 of the Treaty of Tripoli, signed 1796, ratified 1797.
The Democratic Party of the United States has recently come under attack by a number of pundits as a "secular" party--one that derives much of its support from folks that don't go to church much (if at all), and one that tends to run candidates that don't discuss their faith openly. I (along with most liberals) don't find this trend disturbing--indeed, we find it entirely in accord with America's long tradition of separation of church and state.
To understand why we have such a tradition, it's important to remember that the founding fathers were Englishmen, with a rich sense of the debacle that state control of religion had created during the reign of the Tudor and Stuart monarchs. Moreover, the Union was to be of states with a variety of religious traditions: Puritan Massachusetts, Catholic Maryland, and so forth. The first amendment allowed the states to unite without a messy, destructive fight over which faith would become the "official" doctrine.
Have two hundred years of official governmental neutrality on religion crippled American Christianity? If anything, the opposite is true. America is easily the most religious first-world nation. Indeed, this is true even after forty years in which the first amendment has been interpreted more strictly than ever before (for much of our history, many individual states used the school system to teach a sort of generic Protestantism--this was the origin of the outstanding system of Catholic private schools in this country.)
Official secularism is no threat to religion in this country. Instead, it leaves religion free to persuade (judging by the results, religion can be very persuasive indeed).
Where do secularism and religion collide? I can think of four main issues: prayer in public schools, religious displays on public land, abortion, and homosexuality ("blue laws"--laws enforcing public morality--would once have been a fifth, but I believe a general consensus has emerged against these). I'll talk about each specifically in future posts. In general, though, liberals believe that preventing religion from entering the public sphere protects its ability to work privately.