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CHICAGO - Mitt Romney, in his bid to retake the momentum in the Republican primary  from Rick Santorum with a win next week in Illinois, arrives in Chicago on Friday. But the city's mayor - and former White House chief of staff  Rahm Emanuel - couldn't wait to rip into the GOP front-runner,  saying  Romney lacked "the fortitude,  strength or character"  to serve in the Oval Office.

"Now I'm not going to give advice to Republicans. They don't take it and I don't want to give it. They'll make whatever decision they want to make," Emanuel said at an event Thursday morning in Chicago. "You just take a look at the fortitude, the strength, the determination and the vision the president made on the auto industry and juxtapose it to Mitt Romney, who doesn't have the fortitude, the strength or the character in my view to stand up to Rush Limbaugh. How can he stand up and make a decision to save 1.3 million manufacturing jobs?

"That Oval Office requires vision. That Oval Office requires spine. That Oval Office requires determination and grit. Mitt Romney says, 'Let it go.' The president said the American workers are too important to let go, and he doubled down on the American workers. When a decision comes to the Oval Office, who's got the fortitude, who's got the grit, who's got the determination and who's got the back of the American people and middle-class families? And nothing coming into that Oval Office is easy. It's not clear. And I think when you see the character, the fortitude and the strength measured up, and the determination to reject conventional wisdom and see around the corner what's right for the American middle class, people who work every day, play by the rules, you'll see the difference of the two individuals and their vision for America."

A reporter  followed up by pointing out to Emanuel that Bill Maher had made comments that some people found as insulting as Limbaugh's. Limbaugh was ripped by liberals for insulting Georgetown law student Sandra Fluke, while Maher has caught flak from conservatives for  remarks he made about former Alaska Gov. Sarah Palin.

"I thought what Rush Limbaugh said was … absolutely not only wrong, it was absolutely repulsive," Emanuel said. "That said, if you can't stand up to Rush, how are you going to stand up to Russia? And I just don't see it. I'm just telling you, having advised two presidents, and I think I'm very fortunate, it takes fortitude in the Oval Office, it takes strength, it takes determination, and the two individuals - the president of the Unites States and Mitt Romney - had a different vision when it came to the auto industry, and I'm saying the Oval Office requires a person of character to make those calls."

Earlier at the event, Emanuel  defended Obama's actions in addressing the nation's economic crisis.

"The president has, I believe, a case to make about the country he inherited and the early-stage progress we're making getting the economy moving," Emanuel said. "We've talked about it, what had happened …  two months before he was president: The entire financial sector had frozen up, the auto industry was literally within weeks of absolute collapse and the economy was going headfirst past a great recession into a small depression. And he - through sheer will - rejected the conventional wisdom on the auto industry, rejected the conventional wisdom on the financial sector, on the overall economy. …  He inherited an economy that was losing on a monthly basis 650,000 jobs and at least in the last six months is now creating 200,000 jobs. That's an 800,000 job swing.

"When he was thinking about trying to help the auto industry restructure some of the things the industry had refused to do for 30 years, he rejected the advice of 'Let it go bankrupt.' He rejected the advice - which wasn't clear then - on 'Let Chrysler go is the best way to save GM.' That was 1.3 million manufacturing jobs, and he rejected the advice that was screaming into the Oval Office. You have to have the fortitude to believe in what you're doing and see through the cloud and the yelling and screaming to what was right."

On Friday, the president returns to Chicago for a fundraiser, the same day Romney makes a campaign stop in the Windy City. "I'm glad he's coming home to Chicago.  And he is from Chicago, so he's coming home," Emanuel said of his former boss. "I think that's always exciting for us."

The Illinois Republican primary is next Tuesday, and polls currently show a close race between Romney and Santorum.

Matthew Jaffe is covering the 2012 campaign for ABC News and Univision.