It's all supposed to be about campaign promises. Didn't Barack Obama promise to deliver an address from a "Muslim capital" in his first 100 days? It's got to be in a safe, moderate country, of course, but where better than Mustafa Kemal Ataturk's secular/Islamist nation of Turkey, whose rulers talk to Syria as well as Israel, Iran as well as Iraq? But when the Obama cavalcade turned up in the heart of the old Ottoman Empire last night, he and all his panjandrums were praying that he did not have to use the "G" word.

The "G" word? Well, if it doesn't trip him up in Turkey today, Mr Obama is going to have to walk into a far worse minefield on 24 April when he has to honour another campaign promise: to call the 1915 massacre of 1,500,000 Armenian Christians by Ottoman Turkey a "genocide". Presidents Clinton and Bush jnr made the same pledge in return for Armenian votes, then broke their solemn promise when Turkish generals threatened to cut access to their airbases and major US-Turkish business deals after they were in office.

This is no mere academic backwater into which Mr Obama must step but a dangerous confrontation with the truth of history, an explosive swamp of bones and old photographs – along with a few still-living survivors – through which he must either walk with dignity or retreat with shame; and the entire Middle East will be watching the results. For the Palestinians – most of whom, ironically, are Sunni Muslims, the same religion as the Ottoman Turkish murderers – it is a crucial issue. For if Mr Obama cannot risk offending America's Turkish allies about a 94-year-old persecution, what chance is there that he will risk offending America's even more powerful ally, Israel, by condemning the Israeli occupation of Palestinian land, the ever-growing illegal Jewish settlements on the West Bank and the constant destruction by Israel of Palestinian homes that prevent the creation of a Palestinian state?

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Starting on 24 April 1915, Enver Pasha's Turkish army and militias rounded up almost the entire Armenian community, massacred hundreds of thousands of men and sent vast death marches of women and children into the deserts of Anatolia and what is now northern Syria. Expert historians, including Israel's own top genocide academic, insist that the shooting-pits, the organised throat-cutting, the mass rapes and kidnappings – even the use of primitive suffocation chambers – all constituted a systematic genocide.

And it is important to record exactly what Mr Obama said on his campaign website in January 2008. "The Armenian genocide is not an allegation, a personal opinion, or a point of view, but rather a widely documented fact supported by an overwhelming body of historical evidence. America deserves a leader who speaks truthfully about the Armenian genocide and responds forcefully to all genocides. I intend to be that president." Which pretty much locks up any attempt to wriggle out of the promise. Or so you would think.

But already the administration's soft shoes have been trying to finesse away the pledge. "At this moment," Mike Hammer, a White House National Security Council spokesman, said last month, "our focus is on how, moving forward, the US can help Turkey and Armenia work together to come to terms with the past". That Mr Obama should allow such a statement to be made, along with the usual weasel clichés about "moving forward" and "coming to terms", speaks volumes.

Neither the Palestinians nor the Arabs in general have tried to – or should – compare the 1915 slaughter with Israel's treatment of the Palestinians, but there are some faint historical mirrors which rightly worry them. The Turks allege that they began killing Armenians in the city of Van because Armenian insurgents, backed by a regional superpower, in this case, Tsarist Russia, attacked the Turks of eastern Anatolia. Israel claims it bombarded Gaza last December and January because Palestinian "terrorists", backed by a regional superpower – Iran – fired rockets at Israelis.

The political parallels are not exact, of course, but Israel can in any case scarcely debate them when it officially refuses to acknowledge the Armenian genocide in the first place.

But for Mr Obama, there are more pressing points. US and Turkish officials are already discussing how Ankara can help in a US military withdrawal from Iraq, and Mr Obama desperately wants Turkey to help open up the Muslim world to his government to staunch the massive wounds the Bush administration inflicted.