In an impromptu news conference at the White House, Obama said he felt "very comfortable with the fact that when you look at the campaign we're running, we are focused on the issues and the differences that are important to working families all across America."

The Republicans have been accusing Obama of running a negative campaign, focused on attacking his Republican challenger Mitt Romney, especially on Romney's tenure at the private equity firm Bain Capital and his reluctance to release tax returns, than talking about issues important to the American people.

Obama said he and Romney have different visions on how to fix the economy, Medicare, taxes, energy and education, adding "that's what I talk about on the campaign."

Answering questions raised by reporters, Obama noted pressing Romney to release tax returns is not "in any way out of bounds," saying "if you want to be president of the United States, then your life's an open book when it comes to things like your finances."

"People want to know that everybody's been playing by the same rules, including people who are seeking the highest office in the land," said Obama.

Obama also used the opportunity to jab at Republicans, denouncing comments of Missouri Republican Senate candidate Todd Akin about "legitimate rape," calling them "offensive."

Akin, a U.S. Representative who's seeking the Senate seat held by Democrat Claire McCaskill, told a Sunday interview that a woman 's body could prevent pregnancy in the case of a "legitimate rape. " The comments caused a firestorm, and could potentially reverse the race between Akin and McCaskill, which Akin leads.

Obama, who held advantage over Romney in female voters, criticized the flap Monday by saying "we shouldn't have a bunch of politicians, a majority of whom are men, making health care decisions on behalf of women."

"Rape is rape, and the idea that we should be parsing and qualifying and slicing what types of rape we're talking about doesn't make sense to the American people -- and certainly doesn't make sense to me," said Obama.

Asked if Republicans should pressure Akin to quit the campaign in favor of another GOP candidate, Obama said: "I'll let them sort that out."