Tough. It was his job to appoint someone to the position and he did.
Commentary points out the Senate Democrats strategy and the flaw of it:
The Senate Democrats seem to be banking on a scheme to “investigate” the matter, wait for Blago to be impeached and then seat the new appointee selected by the Lt. Governor. But wait. Under Burris’s reasoning he is already the junior Senator from Illinois. No matter what happens to Blago in a few weeks or months, the seat won’t be open again until 2010.
That is a good point, the Senate Democrats decided to play their little power trip game and lost, now they are full of grumbling and beating their chests, but there is nothing they can really do about.
As Burris said "We think they will come around and recognize that the appointment is legal and valid and I am the junior senator from Illinois," and he is right.
They can foam at the mouth all they want, but in the end, Burris is the Senator because legally Blagojevich had the right to appoint him.
The rest is nothing more than posturing.
More on Burris' take on this over at Wall Street Journal.. "Blagojevich Appointee Touts His Credentials and Questions the Legality of Preventing Him From Filling Seat Vacated by Obama."