JOHN C. CALHOUN IS BACK with a vengeance, warming the hearts of Old South romantics while chilling the blood of modern liberals. He conjures up images both appealing and appalling: old-fashioned patriotism, partisan demagoguery, genuine fears, love of liberty. The modern Tea Party movement owes much of its inspiration to the Ron Paul campaign, the only national effort in recent years to mention the Tenth Amendment. Yet inevitably talk of nullification evokes memories of Calhoun and the Lost Cause--even though the roots of the idea run much deeper. The re-emergence of nullification--the repudiation or ignoring of a federal law by a state government--poses an interesting challenge to the power of the federal government and its monopoly on constitutional interpretation.