North Korea just blew up the cooling tower on its own Yongbyon reactor, as part of an ongoing dismantlement deal with the United States. This is a momentous step because it's largely irreversible: North Korea will never again be able to kick out inspectors and start reprocessing plutonium in a matter of days, as it did in 2003.
Of course, we don't know if Kim's decision was affected by the fact he now has a nuclear arsenal. North Korea may very well renounce its nuclear program, but keep the 8-15 bombs it produced during George Bush's "I'm not talking to you" phase (cir. 2001-2006).
By pursuing that ridiculous policy, George W. Bush may have perversely increased America's long-run incentive to prop up the North Korean regime--since now, a coup or political meltdown would run the risk of putting those nukes in the hands of terrorists.