He resigned in a hurry from his UN job in 2005, no doubt passed over for a cabinet job like Secretary of State. Now's Bush's chance to bring him--and mainstream thinking--back into the administration. I think he'd get confirmed without too much trouble by the Senate, especially since Danforth used to serve on the Judiciary Committee...and according to CNN, he told Bush that he would be available for "short-term assignments". With only 18 months left in the administration, sounds like a perfect match.
Here's a link to Danforth's Wikipedia entry.