Talking Points Memo has broken this story as far as I can tell. Scott Brown had asked for "unprecedented" demands.
First, Brown’s campaign manager Jim Barnett said in an open letter to the institute that Kennedy’s widow and president of the board of trustees, Vicki Kennedy, should not endorse a candidate in Brown’s race with Democratic nominee Elizabeth Warren, in order to assure the campaign of the institute’s neutrality.
And second, the Brown campaign wants MSNBC to withdraw as a sponsor:
Furthermore, while we accept Tom Brokaw as a moderator, we prefer debates with local media sponsors, not out-of-state cable networks with a reputation for political advocacy. We are confident that issue can be easily addressed as there are a number of Massachusetts media outlets that would be willing to sponsor a debate such as the one you are proposing for the Kennedy Institute, and I’m sure they would be pleased to have Mr. Brokaw as moderator.
The Kennedy Institute today told the campaign today that they could go jump in the lake.
So now Scott Brown has taken his toys and gone home.
I smell fear.