CHICAGO  The call by Prime Minister Nuri Kamal al-Maliki for a timetable for the removal of American troops from Iraq presents an enormous opportunity. We should seize this moment to begin the phased redeployment of combat troops that I have long advocated, and that is needed for long-term success in Iraq and the security interests of the United States.

The differences on Iraq in this campaign are deep. Unlike Senator John McCain, I opposed the war in Iraq before it began, and would end it as president. I believed it was a grave mistake to allow ourselves to be distracted from the fight against Al Qaeda and the Taliban by invading a country that posed no imminent threat and had nothing to do with the 9/11 attacks. Since then, more than 4,000 Americans have died and we have spent nearly $1 trillion. Our military is overstretched. Nearly every threat we face  from Afghanistan to Al Qaeda to Iran  has grown.

In the 18 months since President Bush announced the surge, our troops have performed heroically in bringing down the level of violence. New tactics have protected the Iraqi population, and the Sunni tribes have rejected Al Qaeda  greatly weakening its effectiveness.

But the same factors that led me to oppose the surge still hold true. The strain on our military has grown, the situation in Afghanistan has deteriorated and we’ve spent nearly $200 billion more in Iraq than we had budgeted. Iraq’s leaders have failed to invest tens of billions of dollars in oil revenues in rebuilding their own country, and they have not reached the political accommodation that was the stated purpose of the surge.