April, as Christopher Hitchens used to put it, is the cruelest month for Armenians.

It is their annual reminder of the 1915 genocide by the Ottoman Empire, in which 1.5 million people lost their lives—starting on April 24 with the roundup of hundreds of intellectuals—and the annual denial by US presidents that it was, in fact, a genocide.

President Obama continued the tradition this year, on the hundredth anniversary of what a US ambassador at the time called "a campaign of race extermination... under a pretext of reprisal against rebellion."

This is a cold, realpolitik flip for Obama, who promised in 2008 to recognize the Armenian genocide as such if elected president. "The Armenian Genocide is not an allegation, a personal opinion, or a point of view," he wrote as a senator, in support of an Armenian Genocide Resolution, "but rather a widely documented fact supported by an overwhelming body of historical evidence. The facts are undeniable."

Clearly, not "undeniable" enough.

Why has Obama changed his position? "That is such an easy question to answer," says Victoria Suner, who is organizing a commemoration of the genocide today at noon at Westlake Park. "Geopolitics. He sees Turkey as an ally in the Middle East" and the antechamber of the Muslim world. (Israel also declines to recognize the genocide, apparently for its own realpolitik reasons—it imports 40 percent of its oil from Azerbaijan, which is politicallly close to Turkey and has territory disputes and border skirmishes with Armenia.)

But Suner points out that that politicians large and small are showing their support on the hundred-year anniversary, from Senator Maria Cantwell to Mayor Ed Murray, who declared today Armenian Genocide Remembrance Day. (More odious politicians are also acknowledging the genocide, including Vladimir Putin and Ted Cruz.)

Why does it matter that Obama and other world leaders recognize the fact of the genocide? Pope Francis recently angered Turkey by acknowledging it, saying: "Concealing or denying evil is like allowing a wound to keep bleeding without bandaging it."

And it's not just about principle. Back to Hitchens: "The original crime, in other words, defeats all efforts to cover it up. And the denial necessitates continuing secondary crimes." He points to Orhan Pamuk being "dragged before a court" in 2005 for acknowledging the genocide, and Turkish Armenian editor Hrant Dink, who was convicted of "insulting Turkish identity" for talking about it and then murdered in front of his newspaper office. (Police later posed with the teenage suspect and a Turkish flag.) As recently as 2010, Turkish president Tayyip Erdogan threatened to expel 100,000 Armenians living in the country, saying: "Tomorrow, I may tell these 100,000 to go back to their country, if it becomes necessary."

The word "genocide," incidentally, was coined by law professor Raphael Lemkin, who said in an interview a few years afterward: "I became interested in genocide because it happened so many times... First to the Armenians, then after the Armenians, Hitler took action."

When I asked Suner why it was important to recognize the genocide, she said: "The question is ludicrous—1.5 million people lost their lives."