Via WaPo:

[S]aturday turned to Sunday, and Republicans had still not heard a response to their last offer. Nothing at 11. Nothing at 12. McConnell decided something was wrong. “We couldn’t get the majority leader to counter,” the GOP leader said later. There were now less than 36 hours until the deadline. “The clock was ticking and we were not moving.”

They weren’t moving because Democrats had decided that they had gone as far as they could. Reid and Obama had disagreed privately about what their next offer should be. At one point, Reid was unhappy with an idea that Senate aides said came from Obama — to put the change in Social Security benefits back on the table in exchange for a delay in spending cuts and a rise in the debt limit.

Aides said Reid actually tore up the proposal and threw it into the blazing fire in his ornate green marble fireplace. The paper burned. Reid said he didn’t want evidence that the idea had ever been considered.