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In late September, when polls were still giving him the edge in several swing states, Mr. Obama bounded onto the stage during trips to Ohio and Virginia, smiling and joking about the NFL needing to get back to regular referees and offering light talk about the Democratic convention and first lady Michelle Obama’s speech there.

But in recent appearances, the president has been mostly all business. While he noted that his and his wife’s anniversary fell on debate night, he omitted a joke he told the night before about Mr. Romney outperforming him, which made a.m. headlines.

He also mentioned a date night he had with Mrs. Obama over the weekend in Georgetown, but only to drive home a larger political point. While he was signing the check, he said, the waiter, an unobtrusive young man, thanked him for saving his mother’s life after she had a stroke because she didn’t qualify for Medicare. Because of the president’s 2010 health care law, he said, the waiter told him she could get insurance and pay for her medications.

“Every time I have a conversation like that, it reminds me that what we do is not sport,” he told the crowd. “It’s not simply who’s up and who’s down, and the polls and how much money is raised and so forth. Ultimately, it’s about that young man and his mom, and the belief that in this great country of ours we’re going to make sure that every single person is treated with dignity and respect.”