We talked yesterday with David Sanger, who writes for our partner The New York Times, about the very disturbing notion that North Korea has already become a nuclear power, and the possibility that Pyonyang could sell nuclear materials to enemy nations, or even terrorists. Sanger wrote his article with his colleague William Broad, who has another article in the Times today about whether Americans would know what to do in order to try and survive a nuclear bomb attack.

It's a simple question with an infinitely complicated answer: what happens if Iran is able to build a nuclear weapon?

Russia is expected to deliver low-enriched uranium to Tehran to bring the Bushehr reactor, Iran's first nuclear power station, online. And the U.S., Israel and other nations are reportedly on alert, as hawks are calling for the bombing the reactor before the fuel is loaded into it.

Sixty five years ago today, the United States dropped the first atomic bomb on Hiroshima. In a public statement justifying the use of the bomb that August, 1945, President Harry Truman said, "The world will note that the first atomic bomb was dropped on Hiroshima, a military base. That was because we wished, in the first attack to avoid, insofar as possible, the killing of civilians."

More than 140,000 people died in Hiroshima. Three days later, the U.S. dropped a second atomic bomb on Nagasaki, killing 70,000 people. 

North and South Korea continued to trade diplomatic blows on Tuesday, with South Korea re-designating the North their "principal enemy," a term that Seoul used to use for Pyonyang, but then retired in 2004. North Korea retaliated by cutting ties with the South, calling southern officials "puppet authorities." Brian Myers, professor of international studies at Dongseo University in South Korea, joins us from the ground with a look at the latest news.

The ongoing back-and-forth between the U.S. and Iran over the latter's nuclear ambitions is often compared to a chess game. But there's a notable difference: a chessboard only has two sides. Yesterday's announcement that Iran would trade in some of its low-enriched uranium for fuel rods to power a reactor that makes medical isotopes - a swap engineered by Turkey and Brazil - had some observers asking what Iran is up to.

President Obama's nuclear summit in Washington has brought together leaders of 47 nations in pursuit of an elusive goal: to lock down unsecured nuclear material within the next four years and prevent it from getting into the hands of terrorists. That agenda would be difficult enough if nuclear material weren't already circulating on the black market, but it is. 

Professor at the Harvard Kennedy School and author of the new report, "Securing the Bomb 2010," Matthew Bunn, joins us to talk about how the U.S. is poised to deal with nuclear threats; this morning's headlines.