President Biden is being showered with congratulations for his statement recognizing the Armenian genocide. It’s bitterly ironic, because human rights abuses on similar scale unfolded while Mr. Biden was vice president and remain under way.

“Beginning on April 24, 1915, with the arrest of Armenian intellectuals and community leaders in Constantinople by Ottoman authorities, one and a half million Armenians were deported, massacred, or marched to their deaths in a campaign of extermination,” Mr. Biden said. “Let us renew our shared resolve to prevent future atrocities from occurring anywhere in the world.”

Said the speaker of the House, Nancy Pelosi, “our hearts are full of joy that President Biden has taken the historic step.” The Senate majority leader, Charles Schumer, tweeted, “This is a step I have long pushed for presidents to take: President Biden is our first president to formally recognize the Armenian genocide.”

Senator Elizabeth Warren, Democrat of Massachusetts, said, “Calling this atrocity what it was — genocide — is long overdue because we must recognize the horrors of the past if we hope to avoid repeating them in the future.”

What use were Biden, Pelosi, Schumer, Warren & Co. between 2011 and today, when the Syrian government of Bashar al-Assad, backed by Iran and Russia, killed half a million Syrians and created 11 million refugees? “Syria Used Chemical Weapons 3 Times in One Week, Watchdog Says,” was the headline the New York Times put over an article that ran inside the newspaper.

How many times in a week would Syria have to use chemical weapons for the story to make it onto the front page, or for Biden, Pelosi, Schumer, and Warren & Co. to support American action decisive enough to bring the use, which has been ongoing for years now, to an end?

In 2016 — while Mr. Biden was vice president — a United Nations panel determined that the Islamic State had committed genocide against the Yazidi minority in Iraq and Syria. A U.N. press release quoted the chair of the Independent International Commission of Inquiry on Syria, Paulo Sérgio Pinheiro, as declaring, “Genocide has occurred and is ongoing.”

Then there are the Rohingya, a Muslim minority in Burma. A December 2018 statement by the Holocaust Memorial Museum found compelling evidence of genocide in that case, too.’

“In August 2017, attacks on the Rohingya community by the Burmese military and others included mass killing, rape, torture, arson, arbitrary arrest and detention, and forced displacement of more than 700,000 people,” the statement said. Where were Biden, Pelosi, Schumer, Warren & Co. on that one?

Probably the best-known recent genocide case is that of the Chinese Communist government’s systematic violence against members of the Uyghur Muslim minority in the Xinjiang region. The American and British governments have both labeled it a genocide.

A recent Nicholas Kristof column in the New York Times described it this way: “Perhaps one million people have been confined to what amount to concentration camps. Inmates have been tortured, and children have been removed from families to be raised in boarding schools and turned into loyal Communist subjects. … Women have been raped and forcibly sterilized.”

There are remarkably few negative professional consequences for American politicians, Republican or Democrat, who allow these genocides to happen, as Mr. Biden’s own career demonstrates. The Biden administration is full of officials who watched ineffectually as Syria deteriorated and the Islamic State rose. Their main policy response seems to be allowing refugees into the United States and delivering hundreds of billions of dollars in sanctions relief to Syria’s strategic partner, Iran.

The best these officials have to offer in their own defense is that the culpability for the genocide lies with the perpetrators, not with the United States. Even as a global superpower, America has practical limits in its ability to intervene to protect civilians.

There’s some truth to both those defenses. There was, though, a moment not all that long ago when instead of pleading helplessness America was acting. It’d only breed cynicism if some day a century from now some future American president is lauded for forthrightness in commemorating a genocide that occurred on Mr. Biden’s watch.

Somehow, the greater the elapsed time between the genocide and the president commemorating it, the more comfortable a topic it is. Mr. Biden’s solicitude for the Armenians is touching, but it comes too late to make much difference. The contemporary genocides and those potentially in the making are the ones that merit urgent presidential preventative attention — while there is an opportunity to affect the outcomes.