Reports streamed into the Situation Room that morning from U.S. diplomats and intelligence officials: Stories of mass executions, women being enslaved as child brides, members of a small religious group trapped on a mountain and potentially dying of thirst.
Then the president, for the first time, was given an assessment that thrust the crisis into a new category.
As one top official put it: ''I had not heard the word `genocide' used in the Situation Room before.''
By the time 90-minute meeting ended, it was clear Obama planned to order humanitarian aid to be airdropped to the Yazidis, a religious minority being targeted by the Islamic State militant group. But advisers were unsure whether Obama would go one step further: airstrikes in Iraq, just three years after the U.S. pulled out from a war that Obama never liked.
As the fast-growing Sunni rebellion overran major Iraqi cities in early June, Obama began weighing his options. A U.S. aircraft carrier was ordered into the Persian Gulf, and Obama began dispatching hundreds of special forces to advise Iraqis and protect U.S. personnel.
On one point, Obama was firm: No ground troops would be returning to Iraq. Yet the prospect of targeted airstrikes hung in the air. Obama was reluctant to take that step, but it could prove critical to preventing a security collapse in Iraq.
In July, some lawmakers were demanding immediate drone strikes, while others were urging the opposite. A top senator threatened to block sales of arms to Iraq, and House of Representatives lawmakers easily passed a resolution to bar Obama from sending forces into Iraq long-term without their approval.
Pentagon leaders were reviewing what U.S. assistance might help Iraq's beleaguered military, while diplomats pressed Iraqi leaders for a political transition that would bring disenfranchised Sunnis and Kurds into the government.
Wednesday was a tipping point. Obama was in three days of meetings with nearly 50 African heads of state who had come to Washington at his invitation. But roughly 6,000 miles (9,655 kilometers) away, the Yazidis were in trouble, having fled to the mountains to escape the extremists.
Senior administration officials met throughout the day at the White House, where they learned that the Iraqis had tried, and failed, to resupply the Yazidis, who were in dire need of food and water.
The Kurds, America's closest allies in Iraq, had sought to hold off the extremists. But on Wednesday, the Kurdish militia started falling back, moving away from Iraq's largest hydroelectric dam as they sought to consolidate their forces to protect the city of Irbil.
Eventually, insurgents took the dam. If fully breached, the dam could flood major swaths of land, endangering the U.S. Embassy in Baghdad.
The chairman of the Joint Chiefs of Staff, Gen. Martin Dempsey, joined Obama for the limo ride back to the White House, where Obama said he knew the Yazidis' humanitarian crisis must be addressed.
By Thursday morning, things had worsened. People were fleeing Irbil. Obama made clear he was inclined to approve military action, officials said. The officials discussed Obama's decision-making on the condition they not be identified.
Obama met for two hours with his team in the Situation Room, where Secretary of State John Kerry and Defense Secretary Chuck Hagel, both abroad, were linked by videoconference. Obama informed his staff he was authorizing two missions: airdrops for the Yazidis, and military strikes in the event Americans were in danger.
Cable news and Twitter soon were abuzz with reports about U.S. military action in Iraq. The White House didn't comment, fearing it could jeopardize the first humanitarian drop, which was underway in Iraq under the cover of night.
Just after 9 p.m., reporters were hastily summoned to the State Dining Room, where Obama spoke to the nation.
''When many thousands of innocent civilians are faced with the danger of being wiped out, and we have the capacity to do something about it, we will take action,'' Obama said. ''That is our responsibility as Americans.''