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From the moment President Obama nominated Jack Lew to be his new Treasury Secretary, it was clear Republicans intended to push back aggressively. It was less clear how. Indeed, the initial complaint -- Lew is too knowledgeable and competent -- needed some work.

But late last week, a new issue came up which is likely to matter in the confirmation process.

As recently as 2010, Jack Lew, President Obama's nominee to be the next secretary of the Treasury, had $56,000 invested in a CitiGroup venture capital fund based in the Cayman Islands' notorious Ugland House, a building whose mailboxes are home to nearly 19,000 corporate entities, many of them tax shelters.

The investment has been in public documents for years and drew no attention when Mr. Lew was confirmed to be deputy secretary of state in 2009 and director of the White House Office of Management and Budget in 2010.

Making political hay out of this may be trickier than it sounds. Indeed, Lew's Republican detractors just spent a year arguing that Mitt Romney's Cayman accounts were unimportant, so it won't be easy for the GOP to turn on a dime and now argue the exact opposite.

Of course, there's a related challenge for Democrats: they not only want to raise revenue by targeting taxes lost to off-shore havens, but they just spent a year arguing that Cayman accounts were necessarily suspect.

All things considered, Lew at least has a reasonable story to tell: he sold his investment three years ago at a loss, he reported all the income, and paid all his taxes. Every aspect of his holdings was disclosed and there was no effort to conceal anything -- which is more than we can say about the most recent Republican presidential candidate. For that matter, the Senate was well aware of Lew's investments when he was confirmed to other posts, making it difficult for his opponents to say they suddenly care about an issue they found trivial just a few years ago.

But perhaps the biggest challenge for Republicans is the creation of a double standard.

As Andrew Kaczynski reported, Hank Paulson had a similar investment portfolio, and the Senate GOP couldn't have cared less.

"He's got to still answer some questions or we may have to postpone the hearing," said [Republican Sen. Orrin Hatch of Utah], who has been critical of Lew's nomination to Politico Thursday. "Right now, I've agreed to the hearing date but it is subject to having answers to the questions that were raised. They aren't difficult to answer, they can answer them."

But when Henry Paulson, then the CEO of Goldman Sachs, was nominated to be Treasury Secretary by President Bush in 2006, Republicans didn't find issues with Paulson's large investments in the Cayman Islands and Hatch gave a statement in support of Paulson's nomination.

Paulson's financial disclosure showed 21 Cayman investments.

There's nothing wrong with holding cabinet nominees to a high standard, but there is something wrong with holding one president's cabinet nominees to a higher standard than previous presidents.

Republicans have already tried to demand information from Chuck Hagel that no other cabinet nominee has ever been asked to provide. The problem will get worse if these same Republicans argue that Treasury nominees from Republican administrations can have Cayman accounts, but Treasury nominees from Democratic administrations can't.