"The greatest failure in American diplomacy, ever"

When Democrats gathered in Boston's boisterous Fleet Center for their national convention, there was, predictably, plenty of talk about Vietnam (John Kerry's old war) and Iraq (George W. Bush's new one).

But down the road at the more decorous Harvard Club, a group of foreign-policy professionals gathered, and their conversation was strikingly different. In a cavernous, dark-paneled room, the sense was that the most grave national-security problems facing the next president lie elsewhere: in North Korea and in Iran and their nuclear programs.

The mood was best captured by Graham Allison, a former Clinton national-security adviser, who declared: "If North Korea succeeds in becoming a nuclear-weapons state, which it could do at any moment...I believe historians will judge that the greatest failure in American diplomacy ever."

That's saying a lot, but the impulse is right. Americans correctly fear more terrorist attacks and more Middle East instability. Both threats will be far more grave if North Korea and Iran go fully nuclear. Yet the Bush and Kerry strategies for heading off calamity differ in significant ways.

In a world that has almost casually accepted Pakistan's and India's open acquisition of nuclear arms, the first question is why North Korea and Iran should strike such fear. Answer: India and Pakistan pose a threat mostly to each other. Iran and North Korea present threats that could ripple out much wider.

If North Korea -- which already claims to have a few nuclear bombs -- goes openly and promiscuously nuclear, dangers soar on two fronts. Asian neighbors that now focus on stopping proliferation might promptly reverse course and join the trend. Japan, South Korea and Taiwan all could embark on nuclear programs in self-defense. The global taboo on nuclear proliferation would go out the window, and America's role as nuclear protector of its Asian allies -- and its associated influence in keeping things under control -- would be undermined.

The far larger danger is that North Korea would develop a cash-and-carry arms program, selling to rogue states and terrorists alike in its desperation to feed itself. As Mr. Allison noted at the Boston event, hosted by the Council on Foreign Relations, the only way to stop that process may be to use military force to destroy the Korean program, "since I can't imagine how if they're running such a production line I can prevent them selling weapons."

Iran isn't as irrational as North Korea but lives in a neighborhood where its decisions may be equally profound. As former national-security adviser Zbigniew Brzezinski notes, Iran's nuclear impulse is understandable. Pakistan and India to its east, Russia to its north and Israel to its west all have nuclear arms. America seeks to set up what Iran sees as client-states on its eastern border, in Afghanistan, and on its western border, in Iraq. Tough neighborhood, Tehran's ayatollahs must tell themselves.

If Iran keeps moving toward a nuclear weapon, Israel may launch a pre-emptive military strike to stop it, as it did against Iraq two decades ago. If Iran crosses the finish line anyway, Egypt and Saudi Arabia, for starters, may decide they also need nuclear arms. Imagine how al Qaeda operatives, who looked to wealthy Saudis for cash, would relish a buildup of nuclear-arms material there.

The Bush formula for dealing with these twin threats is embodied in current policy. Much as he is criticized for going alone on Iraq, Mr. Bush actually is depending heavily on allied help. As recently as Monday, he reiterated that his formula for dealing with North Korea's nuclear program is to avoid direct negotiation with the North and rely instead on the current six-nation talks in which the U.S. is joined by Japan, South Korea, China and Russia in trying to talk down Pyongyang. Mr. Kerry says he'd be willing to talk one on one with North Korea.

Mr. Bush also wants world help on Iran; he leans on the International Atomic Energy Agency to take the lead in either talking down the Iranians or persuading the United Nations to impose sanctions. The IAEA is busy right now trying to figure out whether enriched uranium particles found in Iran are homemade or came in on equipment bought from Pakistan, which will help determine whether a covert Iranian weapons program is proceeding apace. Mr. Kerry more enthusiastically embraces an additional European idea for Iran: offering Tehran nuclear fuel for peaceful purposes and taking back the spent fuel so it can't divert it to build a weapon. A new Council on Foreign Relations study urges going further, into direct talks with Iran.

It's a cliché to say Sept. 11 showed that it's a dangerous world; Iran and North Korea really prove the point. Note to presidential-debate questioners: That deserves much more discussion this fall.

Write to Gerald F. Seib at jerry.seib@wsj.com