They have been waiting since the 2016 campaign, and now the opportunity is finally in sight. When the 116th Congress convenes on January 3, Democrats will at long last have the power to request the Holy Grail of the Trump era: the president’s tax returns. Once the new speaker picks up the gavel and swears in the new Congress, Massachusetts Congressman Richard Neal, the incoming chairman of the House Ways and Means committee, will have unilateral authority to ask Treasury Secretary Steve Mnuchin to “furnish” Trump’s returns. It’s liable to be the definitional conflict of the new Congress. And both sides are already strategizing about how to wage it.

Neal’s initial gambit will be to play nice, and try to get the president to do the same. “One of the things I’m going to try to convince him of is voluntarily relinquishing the documents,” he said in a recent interview. “If you get into a shouting match, he is less likely to relinquish the documents. So we’re going to try, in this case, to convince him to do it, but at the same time prepare the legal case for asking for the documents.” Neal’s hopes for this approach are not very high. “I assume that it is going to be a court case that will go on for a considerable amount of time.”

Since his campaign, Trump has dismissed calls to release his tax returns—bucking decades of political tradition. And Democrats’ sweeping victories in the midterms notwithstanding, Trumpworld has yet to signal a shift in the president’s stance on the matter. “I don’t care. They can do whatever they want and I can do whatever I want,” Trump told reporters the day after the election when asked about the issue. Trump surrogates have predicted a lengthy court battle over the returns. In an October interview, former House Speaker Newt Gingrich warned that if Democrats seek the president’s returns, “They’ll be trapped into appealing to the Supreme Court.” Then, he predicted, “We’ll see whether or not the Kavanaugh fight was worth it.”

Democrats, on the other hand, insist that the the law is on their side. “Legally, it is crystal clear that the chairman of Ways and Means has the ability to get from the I.R.S. the personal tax returns of any individual, including the president,” one Democratic congressional aide told me. Indeed, the relevant I.R.S. provision in the tax code appears to leave little room for Mnuchin to maneuver. “Upon written request from the chairman of the Committee on Ways and Means of the House of Representatives, the chairman of the Committee on Finance of the Senate, or the chairman of the Joint Committee on Taxation, the Secretary shall furnish such committee with any return or return information specified in such request,” it reads.

In theory, that means that Neal doesn’t need a subpoena—merely a written request—to prompt Mnuchin to hand over Trump’s returns. But, as University of Virginia law professor George Yin explained, “All of this is subject to uncertainty because the law is very limited on this authority.” While the Ways and Means Committee should be able to complete the request without “any provocation or condition or limitations” from the Treasury, there’s not much jurisprudence to fall back on—which means plenty of gray area for Trump administration lawyers to kick up dust. The provision has “been rarely used, and the times that it has been used, as far as I know, there has never been any controversy about compliance. [If] a request was made, that request is fulfilled,” Yin continued. “And so in our current situation people are imagining the exercise of the authority and what happens if the secretary of the Treasury refuses.” Notably, there is no rule that provides Mnuchin with a set time line to comply.