To add he was having a full out revolt of his party in the House and Senate.
Sanders, Brown, and Landrieu represent 3 of the groups of the democratic party.
Sanders is an old fashioned liberal, Brown a labor guy from a mid-western state, and Landrieu a southern blue dog.
It would be the equivalent of
DeMint, McCain, and Snowe filibustering a Bush policy.
This stunt was the only way he could capture the news cycle.