The Oct. 3 first of three presidential debates may have changed the dynamics of the race for Ohio’s 18 electoral votes, with President Barack Obama and Mitt Romney both ramping up their appearances in a state that many now say is back in the competitive category.

“I think it’s back in play. That’s why they’re both here. I think they saw enough of a shift in their internal polls,” said Grant Neeley, political science associate professor at University of Dayton. “I think we’re back in play.”

A new CNN poll of likely Ohio voters shows 51 percent backing Obama and 47 percent behind Romney. The four-point lead for Obama is within the poll’s margin of error.

On Tuesday — the last day to register to vote in Ohio — both Obama and Romney were in Ohio, and Romney plans to spend several more days in the state this week, including today in Sidney.

On Tuesday Obama spoke to a crowd of 15,000 students and supporters on Ohio State University’s Oval, pleading with them to register and vote by the 9 p.m. deadline.

“Don’t boo. Vote,” he said repeatedly in response to the crowd. Buses — and Black Eyed Peas star will.i.am — were ready to take students to an early voting site immediately after the president’s 20 minute speech.

Later Tuesday, Romney appeared at a rally in Cuyahoga Falls near Cleveland.

Obama highlighted what he said were the accomplishments from his first term: a 7.8 percent national unemployment rate, the assassination of Osama bin Laden, the end of the war in Iraq, tax cuts for small businesses and middle class families, passage of the landmark health care reform law, the repeal of the military’s Don’t Ask, Don’t Tell policy and reforms that cut out the middle man on student loans so college kids save money.

He criticized Romney’s plan to cut taxes, saying it would grow the deficit or eliminate popular tax deductions for middle class families.

“Gov. Romney said it is fair that he pays a lower tax rate than a teacher or autoworker who makes $50,000. He is wrong. I refuse to ask middle class families to give up their deductions for owning a home or raising their kids just to pay for another millionaire’s tax cut. I refuse to pay for that tax cut by asking you, students, to pay more for college or taking kids out of Head Start programs or eliminating health care for millions of Americans who are poor or disabled or elderly,” Obama said. “And that’s the choice that we face in this election. That’s what the election comes down to.”

Republicans Tuesday said the one-time solid lead Obama had in Ohio is quickly evaporating. Speaking with reporters by phone before Tuesday’s events, Gov. John Kasich said Romney’s solid debate performance energized Republicans and caused independents to give him a second look.

“I think through that debate, he was able to touch people in a way that he hadn’t been able to do before,” Kasich said. “Ohio is doing better — much better than what we were — number 4 in job creation in the country, number one in the U.S., but I always am on edge when it comes to the new job reporting numbers because there isn’t any question that we have a headwind coming from Washington.”

Most pundits quickly declared Romney the winner of the debate, but Obama has since hammered the former Massachusetts governor for misstating his positions and saying he would end federal subsidies for the Public Broadcasting System that airs Sesame Street, starring Big Bird.

“Don’t worry. Somebody is finally getting tough on Big Bird,” the president said Tuesday. “Who knew he was driving up the deficit?”

The Obama campaign released a 30-second TV ad on Tuesday with a deep-voiced narrator seriously intoning: “Mitt Romney knows it’s not Wall Street you have to worry about. It’s Sesame Street.”

Sesame Workshop, the non-partisan, non-profit organization that produces Sesame Street, issued a statement Tuesday asking the campaign to take down the ad.

In an interview with CNN Tuesday night, Romney hit back at Obama over the Big Bird flap: “We’ve got 23 million Americans out of work, or struggling to get a full-time job. We’ve got one out of six Americans now in poverty, 47 million on food stamps, and the president is spending his time talking about saving Big Bird.”

Obama’s appearance at OSU marked his 15th trip to Ohio since Jan. 1 and his 30th since the start of his presidency. Romney’s appearance in Cuyahoga Falls was his 21st trip to Ohio and he’ll add to the count with stops in Delaware and Sidney today and Lancaster on Friday.

Democrats acknowledged Tuesday that the race in Ohio is far from over.

“I think Ohio has always been in play,” said U.S. Sen. Sherrod Brown, a Democrat running for a second six-year term. “President Obama is going to win because the unemployment rate has come down three points, the auto industry is back, we are enforcing trade rules, we have frozen student loan interest rates. The economy is getting better — not fast enough — but the economy is getting better.”

Staff writer Jeremy Kelley contributed to this report.