President Obama, leveraging the stage Monday of a NATO summit in Chicago, defended his campaign critique of Mitt Romney's tenure at Bain Capital -- accusing his likely Republican rival of "missing what this job is about" by touting his experience at the private equity firm. 

At a half-hour news conference covering a host of national and international issues, the president diverted from the security agenda to answer a question about the escalating spat between the Obama and Romney campaigns.

The president said he understands private equity's role of maximizing profits is a "healthy part of the free market." But he said "that's not always going to be good for communities or businesses or workers," and he defended his campaign's decision to scrutinize Romney's Bain record. 

"(Romney's) main calling card for why he thinks he should be president is his business experience," Obama said. 

He went on to say the job of president is "not simply to maximize profits" and that he has to take "everybody" into account -- suggesting Romney would not do the same. 

"And so if your main argument for how to grow the economy is, 'I knew how to make a lot of money for investors,' then you're missing what this job is about," Obama said. 

The Romney campaign responded by accusing Obama of attacking "the free enterprise system."

"What this election is about is the 23 million Americans who are still struggling to find work and the millions  who have lost their homes and have fallen into poverty," Romney said in a written statement. "President Obama refuses to accept moral responsibility for his failed policies."

The comments capped a tumultuous day on the campaign trail, as both candidates traded fire over Romney's Bain record. The Obama campaign on Monday initially found itself on defense, after Obama surrogate Cory Booker, the Newark mayor, criticized the Bain attacks a day earlier. 

But Obama's re-election team stuck with the strategy, releasing a new web video Monday that tied Romney and Bain to an Indiana plant closing two decades ago. 

In response, Romney's campaign released a web video of its own Monday afternoon highlighting the Democratic dissension from Booker and others. 

The video, titled "Big Bain Backfire," featured Booker's comments over the weekend on NBC's "Meet the Press." Booker, who has since walked back his remarks, said Sunday that "I'm not about to sit here and indict private equity." 

The Romney video also featured comments from former Democratic Rep. Harold Ford Jr. and ex-Obama economic adviser Steven Rattner defending private equity and Bain. 

"Have you had enough of President Obama's attacks on free enterprise?" the video asks. 

The Obama campaign, though, was expanding its ad buy from last week spotlighting a steel company that went bankrupt after Bain's involvement. And on Monday, the campaign released another "Romney Economics" web video spotlighting Bain-owned paper company Ampad. 

According to the campaign, the company bought and closed a Marion, Ind., plant in 1994, costing 250 jobs. 

"Bain, Mitt Romney -- they did not care about us as workers. They were looking at the mighty dollar," one former worker in the ad says. 

The ad says Romney and his partners multiplied their investment in the office products plant by 20 times while the company went on to lose some 1,500 jobs and went bankrupt by 2000. 

Meanwhile, Booker continued to take heat for his outspoken comments on Sunday. Despite releasing a three-minute video since those comments walking back his remarks, Obama campaign strategist David Axelrod said Sunday that Booker was "wrong" to say what he did on Sunday. 

"In this particular instance, he was just wrong," Axelrod said on MSNBC Monday. "There were specific instances here that speak to an economic theory that isn't the right theory for the country." 

Obama on Monday called Booker an "outstanding mayor." But he said the Bain issue is "not a distraction." 

"This is what this campaign's going to be about," he said. 

NewsCore and The Associated Press contributed to this report.