President Barack Obama and Vice President Joe Biden are now part of a growing group of Democrats who are aggressively chiding Mitt Romney for not disclosing more information about his personal fortune, estimated as high as $250 million.

The spark that lit the current controversy is "Where the Money Lives," a new Vanity Fair article investigating the role of offshore accounts in Romney's personal finances. "Come August, Romney … will be one of the richest people ever to be nominated for president. Given his reticence to discuss his wealth, it’s only natural to wonder how he got it, how he invests it and if he pays all his taxes on it," Nicholas Shaxson wrote for Vanity Fair.

After Shaxson's piece was published online last week, Democrats "filled the Sunday morning political talk shows citing a Vanity Fair article that suggested Romney's fortune is housed in offshore bank accounts in Bermuda, the Cayman Islands and Switzerland," CBS News reported. "They called on Romney to be more transparent in his finances and release more than one year of tax returns."

One of Shaxson's major talking points is that Romney's father, George, released 12 years of tax returns when he ran for president in 1968 — yet Mitt Romney has released only his 2010 tax returns and subsequently resisted further disclosure. New York Times columnist Paul Krugman seized on that thread in an op-ed piece published Sunday evening: "George Romney was open and forthcoming about what he did with his wealth, but Mitt Romney has largely kept his finances secret. He did, grudgingly, release one year’s tax return plus an estimate for the next year, showing that he paid a startlingly low tax rate. But as the Vanity Fair report points out, we’re still very much in the dark about his investments, some of which seem very mysterious."

On Monday, Obama evoked George Romney during his interview with a New Hampshire TV station. "What's important if you are running for president is that the American people know who you are and what you've done and that you're an open book," Obama said, per USA Today. "And that's been true of every presidential candidate dating all the way back to Mitt Romney's father."

Tuesday morning, Politico obtained an advance copy of Biden's remarks to Hispanic advocacy group National Council of La Raza, which the vice president was scheduled to deliver later that day and which showed he too planned to reference the elder Romney.

The pertinent portion of Biden's prepared text: “When his father, George Romney, was a candidate was for president in 1968, he released 12 years of tax returns because, as he said, ‘One year could be a fluke, perhaps done for show.’ His son has released one year of his tax returns. Making a lie of the old adage: Like father, like son.

“Mitt Romney wants you to show your papers, but he won’t show us his."

Political website The Hill reported that Romney responded to the controversy Monday during an interview with Radio Iowa. "Romney reiterated that his holdings were kept in a blind trust and that he had abided by all U.S. tax laws. 'I don't manage (the holdings),' Romney said. 'I don't even know where they are. That trustee follows all U.S. laws. All the taxes are paid, as appropriate. All of them have been reported to the government. There's nothing hidden there.'"