In an outpouring of rage late Sunday night, a breakaway group set fire to the headquarters of Mr. Morsi’s Muslim Brotherhood movement in Cairo. Hundreds of attackers with Molotov cocktails vowed to kill anyone inside, and used green pen lasers to search for figures in the windows. “Their leaders left them like sheep for the slaughter,” one attacker said. Some Brotherhood members inside fired birdshot at the attackers, wounding several, but there did not appear to be a concerted effort to repel them…

Though angry about the lack of public security and desperate economic conditions, the demonstrators were united in the conviction that Mr. Morsi had failed to transcend his personal roots in the Muslim Brotherhood, an insular Islamist movement that is considered Egypt’s most formidable political force. The sheer scale of the demonstrations across the country delivered a sharp rebuke to the group’s claim to speak for the majority of Egyptians.

“He was of the revolution,” said Magdi Morsi, an airline flight planner demonstrating in front of the palace who is not related to the president. He said he had voted for Brotherhood candidates for Parliament as well as for Mr. Morsi but had turned against them for failing to deliver on their promises. “I decided he was a big liar,” he said. “He must leave. The public is against him now.”