I don't buy the notion, advanced by the McCain campaign, that Barack Obama has been flip-flopping on Iraq, that he has been cutting and running from his long-held antiwar convictions. And I will shortly demonstrate how he has remained broadly consistent. Having said that, however, there's no doubt that Obama is currently doing some nuancing.

Indeed, the facts on the ground in Iraq require that he do so. Domestic political realities also require that he do so.

For instance, there has been a noteworthy change on Obama's official website. Whereas, as recently as 12 days ago, the text stated that "Obama will immediately begin to remove our troops from Iraq," there is no explicit mention anymore of immediacy. The language has been tweaked; a shift in emphasis has occurred.

The old language, as excerpted above, signaled that Obama's 16-month withdrawal clock would start the moment he took office. The new language, by contrast, provides a little more wiggle room: "The removal of our troops will be responsible and phased, directed by military commanders on the ground and done in consultation with the Iraqi government. Military experts believe we can safely deploy combat brigades from Iraq at a pace of 1 to 2 brigades a month that would remove them in 16 months. That would be the summer of 2010..."

In other words, the new passage suggests that, while it would be desirable to pull out the troops on a 16-month timetable that begins on Day One of an Obama administration, the withdrawal clock might not actually start until there is general agreement among the "commanders on the ground," the "military experts" and "the Iraqi government." (It's also worth mentioning that the newly-revised website is not nearly as critical of the troop surge as it was previously. The new language cites an "improved security situation.")

It can certainly be argued that Obama's old language was aimed at the liberal Democratic base, which he needed to win the nomination; and that his new language is aimed at the centrist swing electorate that he needs to win in November. He needs to reassure those swing voters that he would not yank the U.S. out of Iraq in a precipitous fashion, irrespective of ground conditions; in fact, a new national poll reports that only 50 percent of Americans are comfortable with his 16-month timetable stance - a remarkably small percentage, given the ongoing landslide sentiment that the war itself was a mistake.

One can easily recognize this fundamental challenge to Obama's political skills. He has to stick with his basic call for a 16-month timetable (in order to secure his liberal flank), yet, at the same time, signal enough wiggle for the swings.

He sought to do both in his Iraq speech earlier today: "I will give our military a new mission on my first day in office, ending this war. Let me be clear: we must be as careful getting out of Iraq as we were careless getting in. We can safely redeploy our combat brigades at a pace that would remove them in 16 months. That would be the summer of 2010...After this redeployment, we'll keep a residual force to perform specific missions in Iraq: targeting any remnants of al Qaeda; protecting our service members and diplomats; and training and supporting Iraq's Security Forces, so long as the Iraqis make political progress. We will make tactical adjustments as we implement this strategy - that is what any responsible Commander-in-Chief must do. As I have consistently said, I will consult with commanders on the ground and the Iraqi government."

Again, while stating a strict 16-month timetable as a goal, he adds the caveat that any "responsible" president might need to make "tactical adjustments" along the way.

Does all this constitute a flip-flop? A lurch to the center, at the expense of previous left-leaning convictions?

Hardly. There are shifts in emphases, absolutely. But most striking is that what Obama said today, in his Washington speech, and what he said yesterday, in a New York Times op-ed column, remains broadly consistent with what he has been saying over the past several years.

Consider this speech, in November 2006: "I am not suggesting this timetable be overly rigid....The redeployment could be temporarily suspended if the parties in Iraq...offer us a clear and compelling rationale for maintaining troop levels."

Or these remarks, at a Democratic debate last September, when asked whether all troops should be pulled out, or whether some might need to stay: "I think it's hard to project four years from now, and I think it would be irresponsible. We don't know what contingency will be out there. I will drastically reduce our presence there to the mission of protecting our embassy, protecting our civilians and making sure that we're carrying out counterterrorism activities."

Meanwhile, consider what Obama said today about how the money and manpower drain in Iraq is hurting our fight against the terrorists where it counts most, in Afghanistan and Pakistan: "The Taliban controls parts of Afghanistan. Al Qaeda has an expanding base in Pakistan that is probably no farther from their old Afghan sanctuary than a train ride from Washington to Philadelphia. If another attack on our homeland comes, it will likely come from the same region where 9/11 was planned. And yet today, we have five times more troops in Iraq than Afghanistan. Senator McCain said - just months ago - that 'Afghanistan is not in trouble because of our diversion to Iraq.' I could not disagree more....we lack the resources to finish the job because of our commitment to Iraq. That's what the Chairman of the Joint Chiefs of Staff said earlier this month. And that's why, as President, I will make the fight against al Qaeda and the Taliban the top priority that it should be."

And that's precisely what Obama said in a Democratic debate five months ago: "It's important for us not to be held hostage by the Iraqi government in a policy that has not made us more safe, that's distracting us from Afghanistan...I think we have to have more troops there...(The Bush war planners) are hampered now in doing what we need to do in Afghanistan in part because of what's happened in Iraq."

It's true that most Americans now cite the economy, not Iraq, as the top issue of 2008. It's also true that Obama, and Democrats in general, are viewed far more favorably than McCain and the Republicans as potential economic stewards. But it's nevertheless doubtful that Obama can win this election unless he passes the commander-in-chief test - by managing to hold his base on the war and reassure the center, all while parrying the GOP's predictable weakness/flip-flop attacks. His speech today was a recognition of this reality.