Many Senators who support health care reform have made public commitments not to vote for any bill without a public option.  Such pronouncements are not cheap talk.  The pledge can be broken of course but constituents and fellow legislators will hold to account a Senator who breaks it.

And they can be relevant.  A commitment not to vote for the Baucus bill raises the costs of proposing that bill because the pledged Senator would have to be compensated for breaking his pledge if he is going to be brought on board.  In a simple bargaining game, the pledge will be made if and only if the cost of breaking the pledge is higher than the proposer is willing to pay.  In this case the Baucus bill would not be proposed.

But legislative bargaining is not so simple.  Each Senator has only one vote.  A Senator who commits not to vote for the Baucus bill effectively moves the median voter (for that bill) one Senator to the right.  This changes things in three ways by comparison to simple bargaining.

  1. The committed Senator will not be the median voter and so he will not be part of the bargaining.
  2. There is presumably a relatively small gap between the old median and the new so the costs imposed by the pre-commitment are much smaller.
  3. In the event that the gambit fails and the Baucus bill is proposed, it will be a worse bill from the perspective of the gambiteer (it will be farther to the right.)

This means that the commitment is a much less attractive strategy in the legislative setting and it loses much of its relevance.  That is, those who are making this commitment would probably not have been willing to vote for the Baucus bill even without any pledge.