This week, more than any other in recent history, the traditional strategic interests of the United States have veered toward collision with the country's founding principles. President Barack Obama spent the week walking the narrow, dangerous gap between the crumbling edifice of Egyptian autocracy and the potent force of millions of people rallying for American-style democracy and rights - in other words, between the old Middle East policy of self-interested pragmatism and a new one born of principle, devoid of the certainties that had held force since the midst of the Cold War.
To trace that line, all you needed to do was listen to Mr. Obama's fast-changing characterizations of Egyptian President Hosni Mubarak.
Little more than a year ago, the U.S. President was praising the Egyptian autocrat: "He has been a stalwart ally," he told reporters during a warm-hearted meeting with Mr. Mubarak. "I think he has been a force for stability."
On Jan. 28, after hundreds of thousands of Egyptian protesters had filled the streets of Cairo for three days, Mr. Obama still seemed to be on Mr. Mubarak's side, declaring that he must respond with "concrete steps and actions that deliver."
Two days later, he strengthened his tone, calling for "a meaningful dialogue between government and citizens and the path of political change that lead to the future of greater freedom and greater opportunity and justice for the people of Egypt."
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Then the balance shifted, and a different language began emerging. On Tuesday, Mr. Obama seemed explicitly to have abandoned his former ally: "My belief is that an orderly transition must be meaningful, must be peaceful and it must begin now." And then, after Wednesday's violence in Cairo's Tahrir Square, Mr. Obama's spokesman, Robert Gibbs, hammered in the final nail: "When we said 'now,' we meant 'yesterday,' " he said, expressing the President's new position. "That's what the people of Egypt want to see."
For Mr. Mubarak, this was a rather rapid journey from being America's second-most-important military and political client in the Middle East to being an undesirable autocrat. But the transition has been equally abrupt for Mr. Obama, who has transformed from a pragmatic realist who brokered deals based on American interest into something that supporters would call an idealist and opponents have characterized as weak, spineless or confused.
The Obama ideology, for the past three years, has prided itself on a certain calculated practicality, in stark contrast to the regime-changing, change-imposing conservative idealism that defined the George W. Bush years.
The President's Egyptian paradox is only a small part of a larger fissure in the fabric of history, a rupture in the logic that defined the Middle East, leaving him staring out across an empty gulf, devoid of landmarks or handholds, where the rusty scaffolding of foreign policy once stood - a sudden shift of the sort that has not been seen since the end of the Cold War.
This is Mr. Obama's blank-slate moment.
The democratic revolutions in Tunisia and Egypt - with more ruptures likely to follow - coincide with a complete breakdown in the Middle East peace process and the probable demise of America's main Arab negotiating partners in Palestine. There, too, a whole new language will be needed.
An end point was reached two weeks ago when the "Palestine Papers," a large package of peace-process-negotiation documents, was leaked to the al-Jazeera network and the Guardian newspaper.
Western governments have pursued a strategy in which Mahmoud Abbas and his Fatah Palestinian Authority government in the West Bank is given aid and political support, as well as the ever-extended carrot of a potential peace deal and independent Palestinian state, in order to isolate the radical-Islamist Hamas government in Gaza. In short, Mr. Abbas has served a role not unlike that of Mr. Mubarak. And with the leaks, Arabs suddenly saw Mr. Abbas in a very similar light.
They revealed how far Mr. Abbas's negotiators had abased themselves in their effort to reach a deal, any deal, with Israel: They had conceded almost all of the Jewish settlements in East Jerusalem, a traditional Palestinian claim; they had agreed to restrict their long-demanded "right of return" for expelled Palestinians to a limit of 10,000 a year; and they had actively co-operated with Israeli security forces during the 2008 attack on Gaza - and then had been utterly betrayed when Israeli leaders were unwilling or unable, whether through democratic deadlock in their coalition governments or simple stubbornness, to agree to any of it.