One result of the immense attention given to North Korea in 2003 was the start of the Six-Party talks in Beijing between NK, SK, Japan, China, Russia and the US. In 2007 Pyongyang agreed to close its nuclear facilities for emergency fuel aid & normal relations with the US & Japan

NK provided an inventory of its sites but the US said it was incomplete. So, NK refused other meetings. In Feb 2008, Biden, now chair of the Foreign Relations Committee held a hearing on the status of the talks https://www.govinfo.gov/content/pkg/CHRG-110shrg45519/pdf/CHRG-110shrg45519.pdf

Biden gave his views on NK: "Some say we should never negotiate with North Korea, because they can’t be trusted, and this view offers, unfortunately, no viable solution to a problem that got much worse during this last administration, when the administration disengaged."

He went on to criticize more the Bush administration "We wasted... a lot of time, time that North Korea used to acquire uranium enrichment equipment and to more than double its stockpile of plutonium, leading, ultimately, to an actual test of a nuclear device in October 9 of 2006

"There is still, in my view, though, no substitute for patient, principled, sustained, high-level diplomacy. And our efforts are more likely to succeed, moreover, when we enlist those of our allies—South Korea, Japan, and others
of our friends—to help us." Diplomacy with allies.