Washington CNN  — 

Democrats have control of the House, but that may not be enough to get them one thing they really want: access to President Donald Trump’s tax returns.

First as a candidate and now as President, Trump has steadfastly declined to follow his predecessors’ example by releasing his tax returns, leaving details of his business dealings and personal wealth shrouded in mystery.

With Trump’s lawyers threatening a court fight over the release of the returns, Democrats are expected to go directly to the Internal Revenue Service and demand the documents under an obscure law – a move that may not guarantee quick results.

The law specifies that the leaders of the House and Senate tax-writing committees each have the power to request taxpayer information and states that “the secretary shall furnish such committee with any return or return information specified in such request.”

Yet the unprecedented nature of such a request, combined with the political drama surrounding Trump’s returns, would likely draw extended legal review from the Treasury Department.

“Treasury could slow-walk this entire process,” a former senior IRS official told CNN. “There is nothing in the statute that specifies when the agency must comply with the request.”

The decision of how to handle a request for Trump’s returns will fall to Treasury Secretary Steven Mnuchin, one of the President’s closest confidants and earliest backers. A Treasury spokesperson said Mnuchin would review any request for the president’s tax returns with his general counsel to determine if they are required under law.

House Ways and Means chairman Richard Neal has been working to carefully lay the legal groundwork for any request, starting with a subcommittee hearing on a provision in Democrats’ first major piece of legislation, HR 1, that would mandate presidential nominees release three years of their tax returns.

“Well, actually (the) legal case is being prepared and (we are) doing it quite judiciously. (Choosing) our words methodically. This is the beginning of a court case. I think the idea here is to avoid the emotion of the moment and make sure that the product stands up under critical analysis,” Neal told CNN this week. “And it will.”

Democrats have invited Joseph Thorndike, director of the Tax History Project; Steven Rosenthal, a senior fellow at the Urban-Brookings Tax Policy Center; George Yin, a professor at the University of Virginia School of Law and former chief of staff for the Joint Committee on Taxation; and Noah Bookbinder, executive director for the Citizens for Responsibility and Ethics in Washington to testify at the hearing this week.

House Democrats have been preparing for a legal battle since they regained power in the new Congress. It’s unclear whether Democrats would go so far as to request the president’s tax information under subpoena, but there are a number of ways they could put legal pressure on the Treasury secretary, all of which could take years.

That potentially includes holding Mnuchin in contempt or requesting a federal district court to force him to comply with the request, said the former senior IRS official.

The Treasury Department could make the argument that this is the President of the United States and that these returns are so sensitive that it will comply with the request but on a limited basis only allowing members of Congress to view them, rather than making copies that could be disseminated or released to the public, the former IRS official said.

There is some debate among legal experts about whether requesting such information would be considered an abuse of power by Congress by using its oversight for political reasons.

“They are trying to be very careful,” said Kyle Pomerleau, economist at the Tax Foundation. “If they move extremely aggressively quite quickly that could be seen as a political move by Republicans, and that act could lead to ill will in the future.”

Republicans have been quick to jump on that idea, warning Democrats not to overstep.

Staff for Sen. Chuck Grassley, the Republican chairman of the Senate Finance Committee, were briefed last week by the Joint Committee on Taxation about the legal process to obtain the President’s tax returns.

Michael Zona, a spokesman for Grassley, told CNN said the intention of the law was to inform the legislative process not to engage in a “politically-motivated fishing expedition.”

“Those seeking an individual’s personal tax returns to exact political damage would be opening the door to future abuses of power and would poison the public trust in the ability of the IRS to keep personal information private,” said Zona. “That’s an outcome every taxpayer and their elected representative should want to avoid.”