WASHINGTON — President Obama’s campaign is working feverishly to restore its momentum after a lackluster debate performance last week, an effort that began with a conference call 10 minutes before the debate even ended and led to new advertisements, a rewritten stump speech, a carefully timed leak and a reversal of months-old strategy.

Perhaps most important as the president’s team struggles to put his campaign back on track is a renewed effort to win the three remaining debates, starting with Thursday’s face-off between Vice President Joseph R. Biden Jr. and Representative Paul D. Ryan. Mr. Biden began traveling to a Delaware hotel on Sunday for three days of debate camp.

Under the tutelage of David Axelrod, the president’s chief strategist who is personally overseeing the preparations, Mr. Biden will be counseled on how to avoid Mr. Obama’s mistakes and even correct them with a more aggressive prosecution of the Republican ticket. Mr. Axelrod’s involvement highlights the stakes the Obama campaign places on the debate, and Mr. Biden has been reading “Young Guns,” the book co-written by Mr. Ryan, and practicing attack lines that Mr. Obama avoided.

The focus on Mr. Biden comes as the campaign tries to diagnose what went wrong in Denver and what to do about it. Advisers had seen two presidents during practice debates, one who had been listless and passive two nights before and another energetic and aggressive the next night. It turned out the former was the one who showed up in Denver. He kept looking down and was not using the lines they had practiced assailing Mitt Romney, who kept the president on the defensive and presented a forceful case against his re-election.