As expected, President Obama announced today that he plans to withdraw U.S. troops from Iraq over the next 18 months, with a residual force of 35,000 to 50,000 troops remaining until the end of 2011. He did not say whether, if conditions warrant, he would renegotiate the status-of-forces agreement with Iraq, which requires all troops to be out by 2012, although he did say that, pursuant to the current agreements, all troops would, indeed, be withdrawn. He did not say how "combat" ready the residual troops would be. He did not say whether the U.S. would establish semi-permanent bases in the country.

Here's how he explained his decision to an expectant group of Marines at Camp Lejeune in North Carolina.

The president noted that Iraq's own security forces have improved their capabilities, and that violence has dropped sharply in Iraq over the past two years. But the Middle East nation isn't there yet, the president said:

But let there be no doubt: Iraq is not yet secure, and there will be difficult days ahead. Violence will continue to be a part of life in Iraq. Too many fundamental political questions about Iraq's future remain unresolved. Too many Iraqis are still displaced or destitute. Declining oil revenues will put an added strain on a government that has had difficulty delivering basic services. Not all of Iraq's neighbors are contributing to its security. Some are working at times to undermine it. And even as Iraq's government is on a surer footing, it is not yet a full partner--politically and economically--in the region, or with the international community...

What we will not do is let the pursuit of the perfect stand in the way of achievable goals. We cannot rid Iraq of all who oppose America or sympathize with our adversaries. We cannot police Iraq's streets until they are completely safe, nor stay until Iraq's union is perfected. We cannot sustain indefinitely a commitment that has put a strain on our military, and will cost the American people nearly a trillion dollars. America's men and women in uniform have fought block by block, province by province, year after year, to give the Iraqis this chance to choose a better future. Now, we must ask the Iraqi people to seize it.

Obama pledged that his administration will engage Iraq's neighbors--including Syria and Iran--in diplomacy as an effort to keep Iraq secure and maintain stability in the region. The administration will also work with Iraq's government, along with the U.N., in support of national elections. He also suggested direct American involvement in Iraqi politics: "We can serve as an honest broker in pursuit of fair and durable agreements on issues that have divided Iraq's leaders."

For those in the U.S. and around the world hoping for scaled-back American involvement in geopolitics, the kicker: "Every nation and every group must know--whether you wish America good or ill--that the end of the war in Iraq will enable a new era of American leadership and engagement in the Middle East. And that era has just begun."