The Middle East has been a rite of passage for all of America's post-war Presidents. Eager or unwilling, sincere or disingenuous, they have undergone the ritual pursuit of "peace" amid six decades of conflict while protecting the interests, as they defined them, of the United States. All have failed.

As in most things, George Bush kept it simple. Fight in Iraq, corner Iran and defend Israel even when, and sometimes because, Israel's actions were indefensible. Pressed, Bush would talk wistfully sometimes about "the road map", but it was never a route he followed with any great energy. Meanwhile, America's standing among Muslims sank ever lower.

Barack Obama is alert, painfully so, to the fact. He knows that "Middle East peace", a dream older than Israel, is the great prize of any presidency. But first he has to undo the damage wrought by his predecessor, if he can. Then he has to square a dozen circles. Meanwhile, he has a few, just a few, other items on his plate.

That's important, of itself. As Obama sends Binyamin Netanyahu back to Israel with the message that commitments are meant to be honoured, and that a "two-state solution" granting a modicum of justice to Palestinians is the only solution the White House will support, the President has already earned credit. There is economic misery at home. There are legislative battles over health and the environment to fight. He has Iraq and Afghanistan on his hands. He could have postponed the old, intractable problem for another year.

Yet what was it that King Abdullah of Jordan said recently, almost unnoticed by a preoccupied western audience? Simply this: unless progress is made towards a settlement between Israel and the Palestinians, war will resume within 18 months.

The portents are dire. Israel argues that Iran could have an offensive nuclear weapons capability within a year and a half, and threatens a pre-emptive strike. In Gaza, despite a bloody Israeli invasion, Hamas is intact and could yet resume its missile attacks.

Israel, meanwhile, continues to allow settlements to be built on "disputed" (Palestinian) land. Yet the Palestinians themselves are divided. Iran's eccentric and anti-Semitic Mahmoud Ahmadinejad faces re-election next month, with unpredictable consequences. And the newly-elected Netanyahu, always belligerent, has conservative coalition backers who regard compromise - meaning the very idea of an independent Palestinian state - as a betrayal. Nothing is stable.

In that sense, Obama has no choice but to act now. Unlike Bush, he cannot simply blame terrorism and endorse Israel. So the diplomatic effort is stepped up. Netanyahu's visit to Washington will be followed by the arrival of Egypt's President Hosni Mubarak and Mahmoud Abbas of the Palestinian Authority (the West Bank). Above all, the President is expected to fly to Cairo next month and deliver an address, in effect, to the Arab world, both to explain his plans and to mend fences.

Where, he must wonder, to begin? The fist he unclenched towards Iran has not yet been met by an open hand. But Netanyahu, though he laboured the point in Washington on Monday, is not alone in fearing Tehran's ambitions. Sunni Arab states are just as worried, it seems, by the possible emergence of a Shia superpower.

Yet what does that have to do with the Palestinians? Israel would argue that peace is indivisible, and add that Iran sponsors Hamas, and add further that Hamas - like Ahmadinejad - would eradicate the Jewish (as it styles itself) state.

Netanyahu has played diversionary games before, however, as Obama must know. If he forgets, Hillary Clinton, Secretary of State, can remind him. When her husband was in office and the Israeli was last in power, Netanyahu would simply prevaricate, evade and rattle his sabre whenever peace was mentioned. In Washington this week, yet again, he avoided even mentioning a two-state solution.

Consider Israel's arguments, nevertheless. The Palestinians are divided: with whom do you negotiate? Netanyahu's latest coalition is a strange affair, meanwhile, encompassing both the hard right and Ehud Barak's Labour. Halt the settlements and the former would rebel, bringing down the government. In any case, if independence is allowed to Palestine, and if peace breaks out, the "right to return" would become a live issue.

Probably four million Palestinians continue to exist in miserable refugee camps across the Middle East. Many more are scattered around the world. Should even a fraction of those gain the right to return to their ancestral lands, lands within Israel's borders, the Jewish state that America promises to protect would cease to exist. Meanwhile, Syria, another of the west's new friends, would like its Golan Heights, lost in 1967 and annexed in the 1980s, returned. Meanwhile, Israel is beset, as ever, on all sides. And a nuclear-armed Iran waits in the wings.

Israel is adept at these arguments. It tends to overlook the fact, amply demonstrated in Gaza, that there is at present one aggressive regional (and nuclear-armed) superpower. It forgets also that while Prime Minister from 1996-99, Netanyahu wrecked the so-called Oslo peace accords.

He has form. By such means has he built a career.

So, will America call its Israeli client to account, finally? Or will Obama trade? A guarantee to halt Iran in exchange for Palestinian independence? A bout of amnesia over the right of return in exchange for Israeli withdrawal from "disputed" lands? Wider Arab recognition of Israel as a specifically Jewish state, with a right to exist, in exchange for Israel's acceptance, finally, of its obligations?

For now, the President says only that the attempt at "regional peace" has just begun. Netanyahu was also happy to talk peace while in Washington. Everyone in the Middle East talks peace in the lulls between wars. But Israel's Prime Minister still will not accept that Palestinians have a right to a homeland, even to a shrunken, pitiful homeland.

You sense he is wondering how tough this new American President might be, and whether the cost of defying Washington is these days greater than the cost of alienating his support at home. Perhaps President Obama should demonstrate.