President Obama today defended his campaign's persistent demand that Mitt Romney release more than two years of his tax returns, saying it's standard procedure and the American people want to know that "everybody's been playing by the same rules."

"The American people have assumed that if you want to be president of the United States that your life's an open book when it comes to things like your finances," he told reporters in an impromptu press conference at the White House today.

"This isn't sort of overly personal here, guys. This is pretty standard stuff. I don't think we're being mean by asking you to do what every other presidential candidate's done, right? It's what the American people expect," he said.

Romney has said he is following precedent by releasing just his 2010 returns and an estimate for 2011 and that he will not disclose any more than that.

But the president said that wasn't enough. "When it comes to releasing taxes, that's a precedent that was set decades ago, including by Governor Romney's father. And for us to say that it makes sense to release your tax returns, as I did, as John McCain did, as Bill Clinton did, as the two President Bushes did, I don't think is in any way out of bounds," Obama said today.

"The idea that this is somehow exceptional, that there should be a rationale or a justification for doing more than the very bare minimum has it backwards. I mean, the assumption should be you do what previously presidential candidates did, dating back…for decades," he added.

The president's assertion is generally correct, except for Sen. John McCain, R-Ariz., who released only two years of his tax returns in 2008. But McCain was the first candidate to release fewer than five years' worth of returns in more than three decades, according to FactCheck.org.

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In April, Mitt Romney falsely told CNBC that as a nominee in 2004, "John Kerry released two years of taxes." (In actuality, Kerry released returns from 1999 through 2003, and before then had released returns during his Senate races.)

President Obama today brought up Romney's father, former presidential candidate George Romney, Governor Romney's own dad says, "Well, the reason I put out 10 or 12 years is because any single year might not tell you the whole story.' And everybody has, I think, followed that custom every since. "

The president was referring to George Romney in 1967 releasing 12 years' worth of returns because "one year could be a fluke, perhaps done for show."

The president today denied that he was suggesting his opponent had done something illegal.

"The first disclosure, the one year's of tax returns they've disclosed, indicated that, you know, he used Swiss bank accounts, for example. Well, that may be perfectly legal, but I suspect if you ask the average American do you have one, and is that part of how you manage your tax obligations, they would say no," the president said.

-Jake Tapper and Mary Bruce