In January 2007, when General David Petraeus took command in Iraq, he called the situation "hard" but not "hopeless." Today, 18 months later, violence has fallen by up to 80% to the lowest levels in four years, and Sunni and Shiite terrorists are reeling from a string of defeats. The situation now is full of hope, but considerable hard work remains to consolidate our fragile gains.

Progress has been due primarily to an increase in the number of troops and a change in their strategy. I was an early advocate of the surge at a time when it had few supporters in Washington. Senator Barack Obama was an equally vocal opponent. "I am not persuaded that 20,000 additional troops in Iraq is going to solve the sectarian violence there," he said on January 10, 2007. "In fact, I think it will do the reverse."

Now Senator Obama has been forced to acknowledge that "our troops have performed brilliantly in lowering the level of violence." But he still denies that any political progress has resulted.

Perhaps he is unaware that the U.S. Embassy in Baghdad has recently certified that, as one news article put it, "Iraq has met all but three of 18 original benchmarks set by Congress last year to measure security, political and economic progress." Even more heartening has been progress that's not measured by the benchmarks. More than 90,000 Iraqis, many of them Sunnis who once fought against the government, have signed up as Sons of Iraq to fight against the terrorists. Nor do they measure Prime Minister Nouri al Maliki's new-found willingness to crack down on Shiite extremists in Basra and Sadr City?actions that have done much to dispel suspicions of sectarianism.

The success of the surge has not changed Senator Obama's determination to pull out all of our combat troops. All that has changed is his rationale. In a New York Times op-ed and a speech this week, he offered his "plan for Iraq" in advance of his first "fact finding" trip to that country in more than three years. It consisted of the same old proposal to pull all of our troops out within 16 months. In 2007 he wanted to withdraw because he thought the war was lost. If we had taken his advice, it would have been. Now he wants to withdraw because he thinks Iraqis no longer need our assistance.

To make this point, he mangles the evidence. He makes it sound as if Prime Minister Maliki has endorsed the Obama timetable, when all he has said is that he would like a plan for the eventual withdrawal of U.S. troops at some unspecified point in the future.

Senator Obama is also misleading on the Iraqi military's readiness. The Iraqi Army will be equipped and trained by the middle of next year, but this does not, as Senator Obama suggests, mean that they will then be ready to secure their country without a good deal of help. The Iraqi Air Force, for one, still lags behind, and no modern army can operate without air cover. The Iraqis are also still learning how to conduct planning, logistics, command and control, communications, and other complicated functions needed to support frontline troops.

No one favors a permanent U.S. presence, as Senator Obama charges. A partial withdrawal has already occurred with the departure of five "surge" brigades, and more withdrawals can take place as the security situation improves. As we draw down in Iraq, we can beef up our presence on other battlefields, such as Afghanistan, without fear of leaving a failed state behind. I have said that I expect to welcome home most of our troops from Iraq by the end of my first term in office, in 2013.

But I have also said that any draw-downs must be based on a realistic assessment of conditions on the ground, not on an artificial timetable crafted for domestic political reasons. This is the crux of my disagreement with Senator Obama.

Senator Obama has said that he would consult our commanders on the ground and Iraqi leaders, but he did no such thing before releasing his "plan for Iraq." Perhaps that's because he doesn't want to hear what they have to say. During the course of eight visits to Iraq, I have heard many times from our troops what Major General Jeffrey Hammond, commander of coalition forces in Baghdad, recently said: that leaving based on a timetable would be "very dangerous."

The danger is that extremists supported by Al Qaeda and Iran could stage a comeback, as they have in the past when we've had too few troops in Iraq. Senator Obama seems to have learned nothing from recent history. I find it ironic that he is emulating the worst mistake of the Bush administration by waving the "Mission Accomplished" banner prematurely.

I am also dismayed that he never talks about winning the war?only of ending it. But if we don't win the war, our enemies will. A triumph for the terrorists would be a disaster for us. That is something I will not allow to happen as president. Instead I will continue implementing a proven counterinsurgency strategy not only in Iraq but also in Afghanistan with the goal of creating stable, secure, self-sustaining democratic allies.