It is also a day to celebrate a common purpose, said Obama, who is making a rare joint appearance with Sen. John McCain, the GOP nominee, to show unity.  But Obama did not shrink from noting the prickly fact that hangs over every 9/11 anniversary this nation has observed:

Let us remember that the terrorists responsible for 9/11 are still at large, and must be brought to justice.

Obama has also used the attention on 9/11 to reiterate his foreign-policy differences with President George W. Bush and McCain. Responding to a question about Bush and former Mayor Rudy Giuliani, last night Obama told David Letterman:

I think Giuliani deserves credit.  He kept calm and he was clear.  You know, I still remember your show after it happened and how moving that was.  That was one of the most powerful moments on television.  I think that George Bush did the right thing by going after the Taliban in Afghanistan, and I would have done the exact same thing. And the big difference between myself and George Bush I think would have been to stay focused on Afghanistan — not get distracted by Iraq.

I think we would have tamped down Al Qaeda — we could have, if not captured or killed Bin Laden, at least made sure that they weren’t setting up the kind of base camps that have now reconstituted themselves, so they’ve got safe haven in the mountains between Pakistan and Afghanistan.

Sept. 11 is a day to “put aside politics,” says the conventional wisdom. We could all use a break from attack ads.

But it is also a day to embrace American values — which include democracy and robust debate. There may be no better day for Americans to hear out Obama’s foreign-policy arguments, and to consider whether Bush-McCain neo-conservatism has succeeded in catching bin Laden, or going on offense against the right targets. Or making the country safer.