The cruelest thing about politics is that it occasionally gets your hopes up. Sometimes, just when you've almost concluded that the best D.C. has to offer is ringside seats at the latest legislative catastrophe, you get an unexpected outbreak of political courage and common sense.

So it was a cruel trick Sen. Rand Paul, R-Ky., played last Wednesday with his 13-hour filibuster of CIA director nominee John Brennan. For a not-so-brief moment, it seemed possible to restore "normalcy" and bring an end to endless war.

The immediate subject of Paul's marathon session -- whether the administration could legally execute an American citizen on American soil via flying kill-bot -- is, admittedly, an unlikely scenario. Still, I had to laugh when, amid the filibuster, I saw a blog post from the Obamaphilic Center for American Progress, breathlessly warning that the "Number of Radical Anti-Government Groups 'Reached an All-Time High' in 2012." Homeland Security isn't serious enough about fighting "patriot" groups, who fear federal policies "aimed at taking away American freedoms." So send in the drones, already!

But Paul devoted considerable time to a more pressing issue: the increasingly tenuous legal authority for our ever-expanding war on terror. More than a decade after Sept. 11, the legal basis for that war is the Authorization for the Use of Military Force that Congress passed on Sept. 14, 2001, empowering the president to go after those responsible for that atrocity and anyone who "harbored" them.

As Paul noted, "they take that authorization of use of force to mean pretty much anything." We need a serious debate, he said, about "whether that use or authorization of force is open-ended, forever."

Indeed, on the morning of Paul's filibuster, the Washington Post's front page blared: "Administration debates stretching 9/11 law to go after new al-Qaeda offshoots." Actually, they've already stretched it beyond recognition.

As Paul pointed out Wednesday, counterterror mission creep has led to "war in Yemen, Somalia, Mali. It is a war in unlimited places" against increasingly marginal groups that didn't exist on Sept. 11. In Mali, the Post reported, "unarmed U.S. Reapers scour the deserts ... to search for so-called patterns of life -- communications and movements deemed by the U.S. to be telltale signs of militant activity." The targeting information we've passed on has "led to nearly 60 French airstrikes in the past week alone."

Paul raised the possibility of "blowback" from the "inadvertent killing of civilians" -- nearly 200 children in Pakistan alone, for example.

After Paul's filibuster, self-styled "serious conservatives" rose to chastise him. Sen. John McCain, R.-Ariz., who at a 2007 campaign appearance sang "bomb, bomb, bomb, bomb, bomb Iran" to the tune of the Beach Boys' "Barbara Ann," said, "I don't think what happened yesterday is helpful to the American people."

David Frum, author of such conservative classics as the George W. Bush hagiography "The Right Man" and (with Richard Perle) "An End to Evil," insisted that sober, responsible conservatives shouldn't "stand with Rand."

But Paul's concerns echo an older, wiser tradition in American conservatism. In 1967, Russell Kirk praised the late Sen. Robert A. Taft for insisting that war had to be a last resort, threatening as it did to "make the American President a virtual dictator, diminish the constitutional powers of Congress, contract civil liberties, injure the habitual self-reliance and self-government of the American people, distort the economy, sink the federal government in debt, [and erode] public morality."

Does any of that sound familiar?

Sen. Paul has done Republicans -- and the Republic -- a great service by reminding us that there's nothing conservative about perpetual war.

Washington Examiner Columnist Gene Healy is a vice president at the Cato Institute and the author of "The Cult of the Presidency."