In an earlier paper in March, prepared for a workshop on Iraq for the Center for a New American Security, he wrote that "the U.S. should aim to transition to a sustainable over-watch posture (of perhaps 60,000-80,000 forces) by the end of 2010 (although the specific timelines should be the byproduct of negotiations and conditions on the ground)."

He says his article and similar proposals made in scholarly papers and working groups are entirely his own and do not necessarily represent Obama's developing positions about what to do in Iraq.

Certainly, Obama's positions have been evolving though there is no clear sign as yet that he has openly embraced Kahl's recommendations. But he has gone from an "immediate" pullout to one that would remove one or two brigades a month until all combat forces are out in 16 months. Then came his statement that he would consult with commanders on the ground before proceeding with any troop withdrawals.

He opposed the surge at the outset. "I am not persuaded that 20,000 additional troops in Iraq is going to solve the sectarian violence there. In fact, I think it will do the reverse," he said in January of last year. But now, with the picture improving in Iraq, the freshman senator is not so sure of his judgment.

His foreign policy advisers, like Kahl, urge caution. In March, Samantha Power, his former foreign policy mentor, told the BBC, "You can't make a commitment in March 2008 about what circumstances will be like in January of 2009." Last week, Obama's foreign affairs adviser Susan Rice said that "he will listen to his commanders on the ground, he will follow and heed their advice as he decides how at the strategic level we must proceed." Kahl counsels a minimal near-term drawdown to "perhaps 12 brigades" whose mission would "switch to counterterrorism, training and advising of the Iraqi security forces, and force protection for U.S. civilians and advisers."

Such advice represents an abrupt shift away from the rhetoric-filled pullout plans that won over the antiwar base of Obama's party and propelled him to the nomination. That begs the question: what will his disappointed base do now?