The deepening turmoil in Egypt and elsewhere in the Middle East is an especially acute example of an age-old dilemma for the US: how to foster desperately needed social and political change without unwittingly opening the gates of power to hostile regimes in a strategically vital region.
Just a fortnight ago, Hillary Clinton was delivering Washington's bluntest public message in years to rulers of the Arab world. The region's foundations were "sinking into the sand", she warned during a visit to Qatar. Its peoples, especially the unemployed young and a frustrated middle class, "have grown tired of corrupt institutions and a stagnant political order" and were "demanding reforms to make their governments more effective, more responsive and open".
The US Secretary of State was speaking two days before street protests in Tunisia forced that country's president to flee. As always in such moments of ferment, events move faster than the capacity to predict them.
Today, thousands are protesting in Yemen, demanding its President steps down, while the entrenched dynastic rulers of US friends like Jordan and Saudi Arabia wonder if they will be next.
But nowhere are the stakes for Washington higher than Egypt – its most important ally in the region, among the largest recipients of US foreign and military aid, and for all its problems, the Arab world's most populous country and in many ways its cultural and intellectual hub. And no country has so exposed the conflicting pressures the Obama administration is facing.
In 2009, Mr Obama chose Cairo as the venue for his historic speech urging a "new beginning" in relations between the US and the Islamic world – not just its leaders but the ordinary population. But only two months ago, it was acquiescing in Egypt's outrageously rigged elections.
Ms Clinton's own statements this week betray the muddle. On Tuesday, she proclaimed the Mubarak government "stable" and responding to the people. A day later, she was proclaiming her support for "the universal rights of the Egyptian people", while the White House abruptly declined to endorse the Egyptian president. Yesterday, as chaos mounted in Cairo and other Egyptian cities her tone was even more urgent. It was vital for its government to engage with its people. Public grievances ran deep, Ms Clinton said. "Violence won't make these grievances go away."
Her vacillations may be forgiven. The US has often burnt its fingers at similar potential turning points in a region whose pulse it often seems unable to understand.
Less than two years after he "liberated" Iraq, Mr Bush delivered his hubristic 2005 second inaugural address, in which he pledged to spread democracy across the world, not least in the Middle East. A few months later came the Cedar Revolution that seemed to position Lebanon to lead the way in the realisation of this "Freedom Agenda".
In early 2006 Palestine held elections that Washington also insisted be free and fair. What the US got, to its astonishment, was a victory in Gaza by Hamas, regarded then as now by the State Department as a terrorist group. As for Lebanon, the militant Shi'ite Hezbollah movement, backed by Syria and Iran, has a bigger say in national politics than ever.
Iran haunts Washington as it tries to navigate the Egyptian crisis. In the late 1970s a US president committed to human rights prodded an earlier repressive and autocratic ruler – a close regional ally of the US – to embrace liberalisation.
Instead Jimmy Carter was confronted by the fall of the Shah and the arrival of a theocratic Islamic regime that is the sworn foe of America, its influence increased by the US overthrow of Saddam Hussein, and seemingly bent on acquiring nuclear weapons.
Were the current unrest in Egypt to topple President Mubarak, the ideal successor for the US would be a secular democratic moderniser. But there is no guarantee that this will happen.
More likely, Washington would find itself having to deal with the banned Muslim Brotherhood, Egypt's most powerful opposition movement. Of late the Brotherhood has been portraying itself as more democratic. But who knows? Certainly not the US. There is no sign the State Department has a contingency strategy to deal with such an outcome.
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