When believers make political nuisances of themselves, readers can count on one thing: Some editorial writer somewhere will appeal to the "constitutionally mandated separation of church and state."

Listening to the most rigid champions of church-state separation, one could decide that all religiously inspired political speech chips away at the foundations of our democratic republic.

Some Americans may not realize that the Constitution does not refer to "separation of church and state." The First Amendment stipulates that "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof."

The phrase "separation of church and state" appears, rather, in a letter that President Thomas Jefferson wrote to the Danbury (Conn.) Baptist Association in January 1802. In the 200 years since Jefferson wrote that letter, politicians and believers have debated the meaning of his phrase with a passion usually reserved for interpreting Scripture.

Two books published this year will help clarify Jefferson's intent. Despite their plain-vanilla titles and drab covers, Philip Hamburger's Separation of Church and State (Harvard) and Daniel L. Dreisbach's Thomas Jefferson and the Wall of Separation Between Church and State (New York University Press) are vigorous critiques of separationist dogmas.

Dreisbach, a professor in American University's Department of Justice, Law, and Society, writes that Jefferson "saw no contradiction in authoring a religious proclamation as a state official and refusing to issue a similar proclamation as the federal chief executive." Dreisbach further argues that Jefferson's wall separated the federal government from churches and state governments, rather than separating churches ...