COLUMBUS, Ohio—President Barack Obama is recalibrating elements of his campaign, sharpening his stump speech and exploring a new approach for his next debate with Republican Mitt Romney, a sign of how rapidly the presidential contest has shifted in recent days.

Obama speaks during a campaign event Monday in San Francisco. Getty Images

Mr. Obama appears to have absorbed the lessons from his lethargic performance in the first presidential debate. Polls are tightening as Messrs. Obama and Romney battle over about nine states that will decide the Nov. 6 election, including Ohio, where both candidates made appearances Tuesday, the last day residents could register to vote.

Feeling the pressure, Mr. Obama in speeches has begun sounding more optimistic and is snappier in rattling off what he sees as his achievements. He test-drove the new speech Sunday and Monday in California, and continued with the new approach in Ohio on Tuesday. "We have come too far to turn back now," Mr. Obama said at Ohio State University.

Mr. Obama's advisers are also trying to determine how to best prepare him for his next debate with Mr. Romney at Hofstra University in Hempstead, N.Y., next Tuesday. Looking at ways for Mr. Obama to be more aggressive, they considered bringing in Robert Gibbs, a longtime Obama adviser who was White House press secretary until early 2011.

Mr. Gibbs has been seen as one of the few people around the president who can give him criticism bluntly. The campaign said, however, such a move is unlikely.

At the same time, Mr. Romney, seeking to take advantage of his new opening, is striking a softer, more optimistic tone, as the candidates battle for undecided and independent voters. On Tuesday, he noted that he once attended a Christmas party with one of the former Navy SEALs killed in last month's attack on the U.S. diplomatic post in Benghazi, Libya.

When he learned the man had died, Mr. Romney said at campaign stop at an Iowa farm, "You can imagine how I felt." Tuesday night in Cuyahoga Falls, Ohio, Mr. Romney said Americans were increasingly interested in the campaign "in part because people are facing some tough times."

The tone is one way the Romney campaign is seeking to counter a critique from Democrats that the Republican is an out-of-touch businessman. Kevin Madden, a Romney adviser, said the campaign expects a more aggressive tone from the president in the second debate.

During his California trip, Mr. Obama, who will spend the weekend preparing for the debate, got an earful of suggestions for how to approach the next debate. "After the debate, I had a bunch of folks come to me: 'Don't be so polite, don't be so nice,' " Mr. Obama told a San Francisco crowd.

Perhaps the most prominent change in Mr. Obama is his stump speech. Previously, he began with a basic argument that the economy has made progress since he took office but that more work needs to be done.

In recent days Mr. Obama began the speech by reminding audiences that he fulfilled promises to end the war in Iraq, wind down the war in Afghanistan and go after al Qaeda. He also talks about cutting taxes for the middle class, revamping health care and regulating Wall Street, as well as the recent drop to 7.8% in the unemployment rate.

By contrast, at an event in Nevada days before the debate, Mr. Obama didn't mention ending the war in Iraq until more than 2,000 words into his speech.

He has continued to attack Mr. Romney on the stump in a way his supporters wished he had in the first debate, criticizing the GOP nominee's tax plan and accusing him of misrepresenting himself and his positions.

"Get him next week," a woman in the San Francisco audience shouted.

—Laura Meckler contributed to this article.

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