“The ability to find solid blocks of time to do nothing but prepare for debate is almost impossible for a president,” said Dan Pfeiffer, the White House communications director. “The world doesn’t wait for debate prep.”

The president plans to decamp on Sunday to Nevada for a less distracting couple of days of practice.

During preparations, fewer than a dozen advisers are in the room. Senator John Kerry of Massachusetts plays Mr. Romney. Aides press Mr. Obama about unemployment, taxes and foreign policy, and try to be “as annoying as a White House correspondent,” as one put it. “You want to push the button and see how he will react,” the aide said…

Those who have gone up against Mr. Obama said he rarely stumbled over facts but needed to show he understood that voters were hurting.

“Show them personally that you care about them. Empathize,” said former Gov. Bill Richardson of New Mexico, who debated Mr. Obama in 2008. “Take a page from Clinton’s book and say, ‘I feel your pain,’ or something like that.”