APPLETON, Wis. — Republican presidential front-runner Mitt Romney on Friday defended his personal wealth amid intensifying criticism from his main GOP rival and President Barack Obama’s re-election campaign, unlikely allies working to portray the former businessman as out of touch with most Americans.

Romney, who is worth up to $250 million, would be among the nation’s richest presidents if elected. His Democratic and Republican opponents have thrust Romney’s success to the forefront of the presidential contest as he tightens his grasp on the GOP nomination.

“If we become one of those societies that attacks success, one outcome is certain – there will be a lot less success,” Romney said during a speech thick with general election undertones at Lawrence University in Appleton, Wis. “You’re going to hear a deafening cacophony of charges and counter-charges and my prediction is that by Nov. 6 most of you are going to be afraid to turn on your TV.”

The former Massachusetts governor argued his case several days before the GOP primary Tuesday in Wisconsin, a state that has general election implications as he courts working-class voters, who make up the bulk of the electorate.

Obama won Wisconsin by 14 percentage points in November 2008.

Speaking to Wisconsin voters 250 miles to the west, Rick Santorum suggested anew that Romney has little grasp of working Americans’ problems.

“We need someone who can talk and relate to folks battling in this economy, not someone talking about being a CEO of a company and making jokes about firing people,” Santorum said.

“No, I don’t do very well among people with incomes over $200,000 in the Republican Party. Those aren’t the Democrats and independents we’re going to get in the general election,” he said. “We’re going to get the voters Ronald Reagan brought to the table – folks who are blue-collar folks who shared our values but were suspicious Republicans weren’t on their side.”

Though Romney grew up with wealth and privilege as the son of a Michigan governor, he has tried to downplay his early advantages and said in Friday’s speech that he took “an entry-level job” after graduating from Harvard law and business schools.

“I loved cars and I was very tempted to stay in Michigan and go into the car business as he had, but I knew I would always wonder if any success I had was due to my father,” Romney said. “So when I got out of business school, I stayed in Massachusetts where I went to school and got an entry-level job with the best company that would hire me.”