(CNN) -- Mitt Romney returned to his native Michigan on Friday where he created a stir with a comment about birth certificates, reopening a thorny issue pushed by some Republicans who question whether President Barack Obama is a U.S.-born citizen, a requisite for the White House.
Separately, embattled Republican Congressman Todd Akin formally announced that he would remain in the Missouri senate race despite widespread calls from his party to step down after his controversial remarks about rape and pregnancy.
And a new national poll showed Romney and Obama remain deadlocked just days before the opening of the Republican National Convention in Tampa.
Appearing in Commerce Township, Michigan, with his running mate, Rep. Paul Ryan, Romney sought to preview the personal narrative that will be a major focus of next week's nominating convention. He began his stump speech reminding voters of his roots in the Detroit suburbs.
"I love being home in this place where Ann and I were raised, where both of us were born," Romney said. "Ann was born at Henry Ford hospital, I was born at Harper hospital. No one has ever asked to see my birth certificate. They know that this is the place that we were born and raised," he said.
Although Romney was talking about his own birth certificate, the comment amounted to an indirect zing at Obama and the so-called "birther" controversy that has followed him since the last presidential campaign.
The thousands who turned out to see Romney roared at the punch line.
The White House released Obama's full birth certificate in 2011, showing he was born in a Hawaii hospital on August 4, 1961. Only "natural born" citizens of the United States are eligible to be president
In a statement responding to Romney's comments, Obama campaign spokesman Ben LaBolt mentioned real estate magnate Donald Trump and others who have pursued the issue.
"Throughout this campaign, Governor Romney has embraced the most strident voices in his party instead of standing up to them," LaBolt said, adding that Romney's "decision to directly enlist himself in the 'birther' movement should give pause to any rational voter across America."
The Obama campaign used the comment in a campaign appeal to supporters, encouraging them to think about "what he's actually saying, and what it says about Mitt Romney. Then make a donation of $5 or more to re-elect Barack Obama today."
A Romney aide said after Romney's remarks that the former Massachusetts governor has "repeatedly said" that he believes Obama was born in the United States.
"He was only referencing that Michigan, where he is campaigning today, is the state where he himself was born and raised," the aide said.
The comment resonated with some supporters gathered for the campaign event.
"There's been a lot of talk about it one way or another," said Mitzi Pawloski of West Bloomfield, Michigan. "The truth is Obama probably hasn't released all the documents he could."
Others applauded Romney.
"I thought it was great because why should we have to worry about whether the president has a birth certificate or not," said Guy Myers of Clarkston, Michigan.
Michigan is a battleground in November. Obama won the state four years ago and authorized the massive taxpayer-sponsored rescue of failing Detroit automakers and suppliers in 2009. Romney's father was a former auto industry executive and governor of the state. He also sought the Republican presidential nomination in 1968.
New presidential poll shows virtual tie, Akin remains in race
Separately, a CNN/ORC International poll showed Romney and Obama in a dead heat as the campaign approached its fall stretch drive, placing heavier importance on the Republican gathering that starts Monday and the Democratic convention the week after in Charlotte.
According to the survey, 49% of likely voters said they were backing Obama and 47% supported Romney. The margin is within the survey's sampling error, meaning the race is a statistical tie. Further, 48% of likely voters who are independents said they supported Romney, with 45% backing Obama.
In the race for Senate in Missouri, Akin told a news conference that he would not abandon his campaign despite widespread calls from fellow Republicans to do so since unleashing a political firestorm in a St. Louis television interviewed aired on Sunday.
A six-term member of Congress with deep ties to Christian conservatives, Akin initially apologized and said he would not drop out. He made it official on Friday.
"We are going to be here through the November election, and we are going to be here to win," he said.
"I may not be the favorite candidate of some people within the Republican establishment, but the voters made a decision and this is an election, it's not a selection," Akin said.
Republicans have been counting on Akin, who won a three-way primary fight, to defeat incumbent Democrat Claire McCaskill in the campaign considered crucial for any GOP hopes of capturing control of the Senate.
Romney came out more forcefully in an interview, calling the remarks "deeply offensive."
"I can't defend what he said; I can't defend him," Romney said.
More waves before convention, Santorum delegates
With convention planning in the home stretch, Romney's campaign is considering a dramatic scheduling change to guarantee Ann Romney a much larger national audience - but the shift could also cause tensions with a rising GOP star and Latinos, CNN has learned.
If Ann Romney is moved from Monday to Thursday night, she would introduce her husband and bump Sen. Marco Rubio, R-Florida from that role.
GOP sources confirm such a move is under consideration but stress that no final decision has been made.
A Romney campaign spokeswoman declined to discuss any hypothetical scheduling moves.
Ann Romney is considered by many to be one of her husband's strongest surrogates by helping to soften up his image as a calculated businessman.
Convention organizers and attendees also watched to see if a storm churning through the Atlantic with ferocious winds and heavy rains would head for western Florida just as 50,000 people open the convention.
Planners were confident that Tropical Storm Isaac would not disrupt the four-day event and that Romney would be nominated as scheduled.
Romney got some good news on Friday ahead of the convention. Rick Santorum, who at one point was Romney's top challenger for the nomination, officially released his delegates and encouraged them to back the presumptive nominee.
Halimah Abdullah, Kevin Bohn, Peter Hamby, John King, Kevin Liptak, and Mark Preston contributed.