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.

“We will put aside politics and come together to renew that unity, to honor the memory of each and every American who died, and to grieve with the families and friends who lost loved ones,” said both presidential candidates in an unusual joint statement released in advance of the trip.

Even if the plan has mostly noble intentions, however, it is hard to imagine both campaigns completely putting politics “aside” on this one.

President Bush at Ground Zero (WhiteHouse.gove photo)

To the contrary, the very willingness of the GOP to share a 9/11 stage reflects a massive shift in terror politics.

In the last presidential election, Republicans bluntly ran as the party of 9/11. They put their convention in bright blue Manhattan for the sole purpose of making the 9/11 attacks “a primary theme of the convention.”

Sept. 11 was not a day for unity, in the GOP narrative; it was a day when people across the country were “glad” that “George Bush and Dick Cheney were in the White House,” as Lynne Cheney said in her 2004 convention speech.

Now, the Republican nominee presumably sees some gain in appearing with a Democrat on 9/11 — either to show another break with Bush-style politics, or perhaps in the hope that some of Obama’s calm, post-partisan sheen will wear off on him.

No matter what, Ground Zero remains a salient site for political symbolism and images. President George W. Bush’s bullhorn moment, indelibly burned in the public imagination of fans and critics alike, would not have worked anywhere else.

Michael Shaw, a psychologist who dissects political imagery at BagNewsNotes.com, tells TWI the images should be a net gain for Obama:

It puts Obama and McCain on equal footing. In the short run, given the RNC attacks on Obama as an empty suit, the joint appearance in such a solemn patriotic situation — both deriving benefit form the “America first”/ security context — helps level the playing field again.

While the headlines have focused on the nominees appearing together, Shaw predicts another participant could upend things:

The real visual key to the day will be the presence of Hillary Clinton. As N.Y. senator, and the most weighty and compelling female politician in the country, pictures of this emotionally charged and visually compelling event will allow Hillary to substantially return to the media sphere as not just the counterbalance to Palin, but the far more powerful and credible symbol between the two campaigns when it comes to gender politics.

Even putting politics aside, it is sure to be a striking day for politics.