I suppose it’s some comfort that the people calling for Ron Paul’s ouster from the GOP nominating contest are painfully ignorant:

Thomas Jefferson in 1801 launched a preemptive war – without the approval of Congress – against the Barbary States because their actions ran counter to our national security interests.

Where to begin?  Jefferson did order a retaliatory strike against Tripoli in response to the ongoing depredations of Barbary pirates against American shipping, for which he subsequently sought and received Congress’ approval.  That’s what some call self-defense.  Pre-emption implies that a threat was building, and Jefferson acted to eliminate it before it materialised, which is exactly what did not happen.  Our consulate in Tripoli was attacked, and our flag chopped down, which was the quaint local way of declaring war.  The Tripolitanian War was about as “pre-emptive” as the European campaign in WWII.