DES MOINES, Iowa — President Barack Obama and Republican rival Mitt Romney are working feverishly for an increasingly smaller but crucial slice of the electorate — white, working-class voters.

These clock-punching voters — from Iowa’s tiny manufacturing cities to Virginia coal country to pockets of Ohio reliant on the auto industry — are considered the potential tipping point in battleground states that will decide the winner on Nov. 6.  These voters are also critical to turning less competitive states such as Michigan into suddenly swing states in the final stretch.

Romney is trying to expand what polls show is an advantage for the Republican while Obama hopes to narrow the gap. Both candidates are trying to pit these voters against their opponent by stoking a sense of economic and social unfairness, and also by calling on surrogates with stronger ties to these voters. It’s why Romney has seized on Obama’s decision to give states greater flexibility on welfare work requirements and why Obama turned to former President Bill Clinton, long popular with working-class voters, to make the case for his second-term bid.

“In the richest country in the history of the world, this Obama economy has crushed the middle class,” Romney said in accepting the Republican presidential nomination.

Obama counters that Romney’s opposition to a federal bailout of U.S. automakers hurts his chances with working-class whites.

“I stood with American manufacturing. I believed in you. I bet on you,” Obama told an audience in Toledo, Ohio, an automotive manufacturing hub within sight of Michigan, on Labor Day.

These voters are a hodge-podge of union households and gun-rights advocates, often from rural areas and smaller cities. They are found in a handful of competitive states where neither candidate has an appreciable advantage, including northern Florida and northwest and southeast Ohio. They are also found in key counties in states that have voted Democratic in presidential elections since the 1980s but are seen as more competitive this year. Those include areas outside Madison and Milwaukee in southern Wisconsin, mixed-income suburbs outside Detroit and rural parts of western Pennsylvania.

Neither Romney nor Obama has a natural connection with them.

Both are Harvard-educated and wealthy. But Obama, an African American raised politically in Chicago’s Democratic network, has struggled with these voters. Obama famously dismissed their misgivings about his candidacy in 2008, saying “they cling to guns or religion or antipathy to people who aren’t like them or anti-immigrant sentiment or anti-trade sentiment as a way to explain their frustrations.”

Romney, the son of a former governor and car company president, made a fortune as a private equity firm executive before serving a term as Massachusetts governor.

Romney’s profile varies from these working-class voters who are less educated and from smaller cities and rural areas.

He put himself more in league with NASCAR owners, noting his friends who own teams, than fans in February while attending the Daytona 500 in Florida.

But he’ll seek to endear himself again to the sport’s largely white audience Saturday, when he plans to attend the Federated Auto Parts 400 in Richmond, Va.

Still, he has a commanding lead among these voters: 57 percent preferred the Republican, compared to 35 percent for Obama, according to an Associated Press-GfK poll last month. Romney’s support is on par with what 2008 Republican nominee John McCain received from this group, but Obama is doing worse, according to exit polls that showed him at 40 percent four years ago.

Romney sought an edge with Obama’s decision to allow states to apply for waivers seeking flexibility in how to administer welfare work requirements, a key part of the sweeping welfare realignment President Bill Clinton signed in 1996.  

Rick Santorum, who performed well among working-class whites during his unsuccessful bid for the GOP presidential nomination, has led the Romney campaign’s charge that Obama supports lifting the work requirement, a claim widely debunked by independent fact-checking groups.

“(Obama) showed us once again he believes in government handouts and dependency by waiving the work requirement for welfare,” Santorum said during his speech to the Republican convention.

Diane Carnes of Chillicothe, Ohio, in the state’s rural south, said there is a cultural disconnect with Obama. “Southern Ohio is full of people who are disgusted with this president walking away from welfare reform,” said Carnes, a Republican. “We are working people, who believe in work.”

Santorum vigorously dismissed suggestions of racial politics, although Carnes and other Republicans said some rural white voters in swing states still harbor racial opposition to Obama.

Obama’s policies fall outside this bloc’s comfort zone, said Steve Schmidt, who managed McCain’s 2008 campaign.

“President Obama is totally out of touch with these people in a fundamental way,” Schmidt said. “In this environment, Romney’s team is wise to be focused on this group.”

Romney was in Chillicothe, the heart of southern Ohio, last month, promising to loosen restrictions on oil, coal and natural gas development industries. That signals to many voters here the promise of well-paying jobs in counties where unemployment has run well above the state and national averages.

Romney’s choice of Rep. Paul Ryan is seen as another direct appeal. Ryan is from Janesville, Wis., a manufacturing hub between Madison, Wis., and Chicago.

“Remember when he said people in the Midwest, people like us like to cling to their guns and religion?” Ryan said of Obama while campaigning in Iowa this week. “This Catholic deer hunter is darn proud of that. Guilty as charged.”

Many of these conservative Democrats helped elect Republican Ronald Reagan president in 1980.

But since then, a Republican has not won Wisconsin, Michigan and Pennsylvania. Ryan’s place on the ticket, and Romney’s direct appeals to working-class whites, may not tip the state to the GOP in November, but they could force Obama to spend money to capture states critical to his re-election chances.

This voting bloc has shrunk dramatically as a share of the overall electorate, now more diverse and college-educated. In 1980, 63 percent of voters were white, non-college-educated. In 2008, they made up just 39 percent. And Obama performs far better with minority voters.

Obama, in turn, is trying to hold down Romney’s margins. He talks about his wife Michelle’s upbringing in a working-class home on Chicago’s South Side.

His campaign is working to undercut the businessman Romney’s jobs argument by contending that the private-sector experience Romney touts was often at the expense of working families. Romney’s former private equity firm Bain Capital helped launch some national chains, but also shuttered some plants.  

“I continue to believe Gov. Romney is going to struggle in all the Midwestern states given his stance on the issues,” Obama’s campaign manager Jim Messina said in an interview.

Obama also has two weapons in his arsenal and is deploying them strategically.

Vice President Joe Biden, long a popular figure to working-class Democrats, grew up in Scranton, Pa., and has jabbed hard at Romney’s credibility with these voters.   

“Out of touch? Swiss bank account, untold millions in the Cayman Islands. Who’s out of touch, man?” Biden said recently.

Clinton stars in an Obama campaign ad and was the prime-time speaker at the convention on Wednesday night. Clinton’s profile as a former Arkansas governor helped him as a candidate. His wife, Hillary Rodham Clinton, performed better than Obama with working-class whites in places like Pennsylvania and West Virginia during their battle for the 2008 Democratic presidential nomination.

Romney advisers said Clinton is the strongest counter-punch Obama has with these voters.

The former president went hard after them hard in his convention speech, using the term “middle class” no less than 10 times.

Clinton directed his closing pitch to them: “If you want a winner-take-all, you’re-on-your-own society, you should support the Republican ticket. But if you want a country of shared opportunities and shared responsibility, a we’re-all-in-this-together society, you should vote for Barack Obama and Joe Biden.”