On May 15, 2007, at a Republican primary debate in Columbia, South Carolina, longshot presidential candidate Ron Paul shocked the room with his answer to a question about how 9/11 changed America: "Have you ever read the reasons they attacked us? They attack us because we've been over there; we've been bombing Iraq for 10 years."

Then-frontrunner Rudolph Giuliani, visibly agitated, interrupted the proceedings to condemn Paul's "extraordinary statement…that we invited the attack because we were attacking Iraq" and then demand a retraction as the crowd went wild. Campaign reporters, straight and ideological alike, started writing Ron Paul's obituary. But a funny thing happened on the way to Paul's seemingly inevitable ostracism from the Republican Party for the sin of noninterventionism: His star began to rise, while Giuliani's crashed and burned.

Now retired from Congress after a second, more successful run at the White House, Paul can gaze out at a world and a GOP that has become much more sympathetic to his once-lonely view of the world. There are entire armies of young libertarian activists—including many recent military veterans—who got their introduction to the philosophy through Ron Paul's bracing criticism of U.S. misadventures abroad. You can't talk about libertarian foreign policy without talking about—and to—Ron Paul. Reason Editor in Chief Matt Welch caught up with the three-time presidential candidate over the phone in October.