CHARLESTON, S.C. — Looking out from the harbor here, it's easy to imagine a mortar lighting up the night sky as it hurtled toward Fort Sumter and signaled the start of the Civil War. It's also easy, standing inside the walls of the island garrison, to view today's nullification battle over health care less as a frivolous political game and more as a serious threat to the Constitution. "The last ray of hope for preserving the Union peaceably expired at the assault on Fort Sumter," mourned President Abraham Lincoln. Painted on the wall of the fort's small museum, those words...