It’s too bad; a couple more speeches and Obama could have turned him into Bernie Sanders.
As Benen says, it says a great deal about Nelson that he waited until after plenty of money had already been wasted on him and with the window to find a replacement shrinking rapidly. (Even worse, this might result in Bob Kerrey, one of the few political figures distinctly more irritating than Nelson, running for the Dems.) Officially, this is bad news; as always with red-state Democrats, the inevitable Republican replacement will be even worse. But it’s hard to be that upset about it.