Obama will lay out a careful explanation and firm defense of the public option.  He will explain what the public option accomplishes, and why the approaches offered so far that fail to include a public option are deficient.  He will present a checklist of necessary elements of reform, and explain how the public option works to accomplish the elements on the checklist.

He will express strong skepticism, but not outright rejection, of public option "triggers".

He will express strong skepticism, though not outright rejection, of the "cooperatives" alternatives.

He will lay down a challenge to the opponents of the public option.  If you're so smart, what are your alternatives?  Put up or shut up.

By issuing this challenge, Obama will give all the needed ammunition to the defenders of the public option, while at the same time not appearing to take a doctrinairre stance. It is unlikely that opponents of the public option will be able to come up with anything that plausibly meets the necessary conditions for reform on the checklist.  Henceforth, supporters of the public option will be able to reject alternatives by saying, "This proposal fails to meet the president's challenge."

On the other hand, perhaps some genius will be able to come up with an alternative that does all the jobs the public option does, and does them better.  Great.  Have at it.   However, I expect that it will become quickly apparent to most just how difficult and unlikely this is.

By defining the principles of successful reform as the achievement of certain goals, goals that in fact only the public option achieves, Obama can create a political situation in which the public option wins the day, not as as a piece of ideological dogma, but as the only available practical means for achieving necessary reforms.