Only last month, the conventional wisdom was that North Korea was showing promising new signs of moderation, what with Kim Jong Il's parley with Bill Clinton, the release of two American journalists and some South Korean hostages, and a highly publicized meeting between a Pyongyang diplomat and New Mexico Governor Bill Richardson.

On Friday, the charm offensive ended. In a letter to the U.N. Security Council, the North announced that "reprocessing of spent fuel rods is at its final phase and extracted plutonium is being weaponized."...