Edwards seemed to concede, in other words, that his withdrawal policy could precipitate two unacceptable outcomes that would require him to abandon the withdrawal.

So, here is another question for the Democratic candidates: What if it becomes indisputable that the surge is working?

Last month, Gen. David Petraeus, the U.S. commander in Iraq, testified that overall attacks there have been declining. Government Accountability Office data backed him. The Defense Department is now reporting that combated-related casualties in Iraq dropped to 41 in September, the lowest monthly total since July 2006.

A rational basis for skepticism about the surge remains, of course. What if Iraq's sectarian politicians don't exploit the enhanced security created by our military and fail to advance Sunni-Shiite reconciliation? The divided and buffoonishly led Iraqi parliament has failed to pass a single major "benchmark" aimed at that purpose.

Yet, other indicators do point to political progress. As Petraeus told Congress, Sunni tribal leaders have joined with our military to drive al-Qaida out of Anbar, and Shiite warlord-clergyman Moqtada Sadr has called on his militia to suspend its activities.

Then last week, another thing happened. Iraq's Shiite Deputy President Adil Abd-al-Mahdi, a member of the Islamist party formerly known as the Supreme Council for the Islamic Revolution in Iraq, made state visits to Sunni Egypt and Sunni Jordan. There was a Nixon goes to China aspect to this: Abd-al-Mahdi's party, founded in Iran under the inspiration of Ayatollah Khomeini, has been the most entrenched political foe of unreconciled Sunnis.

In a televised press conference in Jordan, Abd-al-Mahdi said the surge was leading to both security and political improvements. "It goes without saying that increasing the number of troops has contributed to the enhancement of security," he said. "Many forces that used to carry arms now believe that political cooperation is the only way for the future." He argued this "allows trust to return among the Iraqis."

Abd-al-Mahdi is positioning himself to be the cross-sectarian leader of a unified Iraq. If the diminishing trend in violence continues, and Abd-al-Mahdi or someone like him gains traction, will Democratic presidential candidates give him, and the U.S. policy that made him possible, credit and support?

Or will they succumb to the temptation to fall back on their 1864 platform?