“You could tell people were itching for a fight,” Mr. Graham recalled in an interview. “The prime minister was a disaster. He kept preaching to me, ‘You can’t negotiate with these people, they’ve got to get out of the streets and respect the rule of law.’ I said, ‘Mr. prime minister, it’s pretty hard for you to lecture anyone on the rule of law. How many votes did you get? Oh yeah, you didn’t have an election.’ ”

General Sisi, Mr. Graham, said seemed “a little bit intoxicated by power.”…

All of the efforts of the United States government, all the cajoling, the veiled threats, the high-level envoys from Washington and the 17 personal phone calls by Defense Secretary Chuck Hagel, all of it failed to forestall the worst political bloodletting in modern Egyptian history. The generals in Cairo felt free to stiff the Americans first on the prisoner release and then on the statement in a cold-eyed calculation that they would not pay a significant cost — a conclusion bolstered when President Obama responded by canceling a joint military exercise but not $1.5 billion in aid.

For Mr. Obama, the violent crackdown has left him in a no-win position: risk a partnership that has been the bedrock of Middle East peace for 35 years, or stand by while longtime allies try to hold on to power by mowing down opponents. From one side, he has been lobbied by the Israelis, Saudis and other Arab allies to go easy on the generals in the interest of thwarting what they see as the larger and more insidious Islamist threat. From the other, he has been urged by an unusual mix of conservatives and liberals to stand more forcefully against the sort of autocracy that has been a staple of Egyptian life for decades.