Last week, Taliban leader Mullah Omar issued a taunting statement warning America about its prospects in Afghanistan. Here's a choice excerpt:

The former Soviet Union claimed, the Red Army was invincible but faced defeat at the hands of the Afghans and completely disintegrated. Many other countries got independence thanks to that. Today USA, the Britain and their allies are bent on subjugating Afghanistan. They are in a total self-delusion and their brain seems not working normally.

This is a season of historical analogies. The one-eyed cleric is hardly the first to invoke the Soviet debacle in his country. Meanwhile, others are warning that to ignore the legacy of Vietnam would also be a sign that our brains are, uh, not working normally. Certainly there are important lessons to be drawn in both cases. But both come with one major difference from the current situation, which limits their applicability. Call it the superpower factor.

Start with Vietnam. Yes, the analogy sounds spooky: The U.S. fought a diffuse guerilla army which enjoyed a sanctuary across the border. But remember: That conflict invloved not just the Viet Cong but also the North Vietnamese army--a fairly professional and well-equipped force. (It was an NVA anti-aircraft missile which brought down John McCain over Hanoi, for instance.) And the NVA had the backing of a superpower: The Soviet Union, which provided them with a steady supply of weapons and financial aid.

That same superpower--the USSR--had a go at Afghanistan a decade or so later, with famously painful results. But the Soviets, too, were fighting a superpower by proxy. By the mid-1980s, America was pumping aid to the mujahideen, including Stinger missiles capable of shooting down Soviet helicopters--a back-breaker for Moscow. Charlie Wilson and all that, with an assist from Saudi petrodollars. (The Soviets also didn't even attempt a real counterinsurgency campaign, about which I've written here and here and here.) Mullah Omar says the Soviets suffered defeat at "the hands of the Afghans," but it's not clear whether the Afghans could have done it without a whole lot of outside help.

Today, America is the world's lone superpower fighting a Taliban insurgency without anything like the support enjoyed by either the NVA or the muj. That makes for a very different situation. It's true, of course, that the Taliban earn millions through the opium trade, get a steady supply of cash-stuffed suitcases from the Gulf Arab states, and, as the McChrystal report asserts, receive aid from Iran and elements of the Pakistani ISI. The Taliban are clearly a formidable enemy, no doubt. And so this analysis doesn't come close to proving that America can win in Afghanistan. But if our brains are working normally, we'll bear in mind the important limitations of these two increasingly-common historical analogies.