The NYT reports (here) that the terms of Clinton's visit had been negotiated for quite some time, with assurances from the North Koreans that Clinton would not leave without Ling and Lee. Clinton was not an "official" envoy of the Obama Administration, but the Times says that Hillary was involved in setting up the trip.
According to the article, Clinton had wanted to visit North Korea (to negotiate re: its nuclear program) towards the end of his Presidency, but he never made the trip as the two countries were unable to come to terms. There is speculation that Clinton and Kim probably discussed the nuclear issue yesterday and this may provide a breakthrough in negotiations.
Maureen Dowd has a good piece this morning (here) about the power of the "Big Dog" (I love that nickname!) and -- in true Dowd fashion -- brings home the personal angle:
Bill had the additional schadenfreude spritz of knowing that he had usurped three men he’d had fraught relationships with — Bill Richardson, Jimmy Carter and Al Gore (whose media company the women were working for) — by getting the high-profile assignment to rescue the damsels in distress.