To hear the critics tell it, the warrantless wiretapping law passed by Congress this weekend is an immoral license for a mad President Bush and his spymasters to eavesdrop on all Americans. For those willing to believe such things, mere facts don't matter. But for anyone still amenable to reason, the deal is worth parsing for its national security precedents, good and bad. The next Democratic President might be grateful.

The good news is that the new law will at least allow the National Security Agency to monitor terrorist...