Following up on an earlier item, as if there weren’t enough questions involving taxes swirling around Mitt Romney, his offshore accounts make his tax returns that much more important.

The Romney campaign has pushed back against the reports this morning, arguing that the Republican is not using his offshore strategy to avoid U.S. taxes. The Wall Street Journal reports the campaign’s line is dubious.

Tax experts said some of the offshore holdings are likely intended to help Mr. Romney avoid paying an obscure but hefty tax of as much as 35% on some of those investments, held in a tax-deferred retirement account.

As The Wall Street Journal reported in Thursday’s paper, many of Mr. Romney’s offshore investments are held through his individual retirement account, which has grown to between $20.7 million and $101.6 million. IRAs are tax-deferred accounts, in which earnings accrue tax-free until the money is withdrawn during retirement.

Mr. Romney’s IRA has grown so large, it appears, due to investments in various vehicles managed by Bain Capital, the investment fund he helped found in 1984. His latest financial disclosure report, filed in August, shows that many of the IRAs assets are in Bain-affiliated entities located offshore, including one in the Cayman Islands that the report listed as having a value of between $5 million and $25 million.

The WSJ report added that if those funds were in the U.S., Romney would likely have been subjected to an obscure levy called the “unrelated business income tax.” By going offshore, Romney is avoiding the tax bill.

It’s hard to say with confidence exactly what Romney’s up to with these investments since he won’t release his returns and as the AP added, “Neither Romney nor his campaign are providing details, including how much he has invested there, or why, or if any of his money is invested elsewhere outside the United States.”

But the story itself has the potential to do some real damage to Romney. Even if we assume the typical voter doesn’t know or care about the nuances of offshore banking strategies, I suspect when the American mainstream hears “guy who keeps money in the Caymans,” questions about trust necessarily follow.

It’s also part of a larger picture. Again, the Republican frontrunner amassed a vast fortune after laying off thousands of American workers, he now pays a lower tax rate than most of the middle class, he wants to give himself another tax cut, he owns multiple luxury homes, and stashes cash in the Caymans — all while pursuing an agenda that would make things tougher on American’s working class.

And the same guy wants to keep the details from the public and refuses to release his tax returns.

I know a lot of news outlets are interested in Marianne Gingrich today, but Romney’s offshore accounts seem like a much bigger deal.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.