U.S. President Obama said on Monday that using Mitt Romney's record at Bain Capital to attack is not a distraction, but part of debate against his rival in the coming election campaign.

In a press conference at the end of the NATO summit in Chicago, the president defended himself against criticism by Cory Booker, mayor of Newark, New Jersey, that Obama reelection team's questioning over Mitt Romney's record at Bain Capital "nauseating" and "a distraction from the real issues."

"Private equity is set up to maximize profits. That's healthy part of free market," said Obama, "but that (maximize profits) is not always good for community."

"When you're president, as opposed to the head of private equity firm, your job is not simply to maximize profit, your job is to figure out how everybody in the country has a fair shot, your job is to retain workers who was laid off, and how to set up an equitable tax system," said the president.

"His (Romney's) main calling card for why he thinks he should be president is his business experience. He's not going out there touting his experience in Massachusetts. He's saying, I'm a business guy. I know how to fix it. And this is his business," said Obama,"if your main argument is how to make a lot of money for investors, then you are missing what this job is about. That's not what my job is as president."

Last week, Obama's reelection campaign launched a television ad campaign highlighting the bankruptcy of a Kansas City steel plant that Bain Capital, the firm Romney led for 15 years, had acquired.

"Mr. Romney is responsible for the proposals he is putting forward for how he says he is going to fix the economy," Obama said, "if the main basis for him suggesting he can do a better job is his track record as the head of a private equity firm, then both the up-sides and the downsides are worth examining."