Can Donald Trump stop Congress from seizing his private business records? He’s certainly giving it the ol’ college try. The Trump family sued their two banks to prevent them from complying with subpoenas issued by House Democrats, a move that will tie up their investigative ends for at least months:

President Trump, his three eldest children and his private company filed a federal lawsuit on Monday against Deutsche Bank and Capital One, in a bid to prevent the banks from responding to congressional subpoenas.

In the suit, filed in federal court in Manhattan, the president and his family members argue that the Democratic House committee leaders who issued the subpoenas engaged in a broad overreach.

“This case involves congressional subpoenas that have no legitimate or lawful purpose,” the suit alleges. “The subpoenas were issued to harass President Donald J. Trump, to rummage through every aspect of his personal finances, his businesses and the private information of the president and his family, and to ferret about for any material that might be used to cause him political damage. No grounds exist to establish any purpose other than a political one.”

As the New York Times notes, this is not the first salvo in the battle. Last week the Trumps sued their accounting firm Mazars USA to prevent their compliance with congressional subpoenas as well. Deutsche Bank is the big prize because they have the longest track record with Trump; they stuck with him even during his massive setbacks in the 1990s. If there’s any dirt to find, it would likely be found there, although at the moment only sheer speculation would prompt anyone to propose it exists at all.

That’s one of the big problems the House faces with these subpoenas. Congress’ power to issue subpoenas isn’t unlimited, especially when it comes to private business records. It still has a long reach nonetheless, as a couple of experts tell the Washington Post:

But legal experts predicted that the courts would be unwilling to stand in the way of congressional oversight. If nothing else, however, the lawsuit could delay the committees’ investigations into Trump’s finances and business dealings.

“This isn’t a close legal question,” said David Alan Sklansky, a professor at Stanford Law School. “I’m quite confident there has never been a situation where a congressional subpoena has been quashed without a finding that it violates a constitutional right.”

The claim that there is no legitimate need for the subpoena, or that it is politically motivated, is a “frivolous argument, even if it’s true,” he said. “That is not a basis for quashing a subpoena.”

Nor is the claim that the inquest violates the privacy of the president or his family members, the law professor said. “That’s how subpoena power works — it’s about getting information that people would like to be kept private,” he said.

The legal question may be closer than Professor Sklansky suggests. There is a reason that the suit frames the objection around their purpose. According to an analysis by the Congressional Research Service in 2017, Congress has far-reaching power to compel testimony and document production as long as their investigation has a “legitimate legislative purpose.” In applying their constitutional responsibility for oversight with government agencies in the executive branch, that writ goes a very long way, but that pretense is gone here:

A committee’s investigation must have a legislative purpose or be conducted pursuant to some other constitutional power of the Congress, such as the authority of each House to discipline its own Members, judge the returns of the their elections, and to conduct impeachment proceedings. Although the early case of Kilbourn v. Thompson held that the investigation in that case was an improper probe into the private affairs of individuals, the courts today generally will presume that there is a legislative purpose for an investigation, and the House or Senate rule or resolution authorizing the investigation does not have to specifically state the committee’s legislative purpose. In In re Chapman, the Court upheld the validity of a resolution authorizing an inquiry into charges of corruption against certain Senators despite the fact that it was silent as to what might be done when the investigation was completed. …

Despite the Court’s broad interpretation of legislative purpose, Congress’s authority is not unlimited. Courts have held that a committee lacks legislative purpose if it appears to be conducting a legislative trial rather than an investigation to assist in performing its legislative function. Furthermore, although “there is no congressional power to expose for the sake of exposure,” “so long as Congress acts in pursuance of its constitutional power, the Judiciary lacks authority to intervene on the basis of the motives which spurred the exercise of that power.”

How does that apply to private-sector businesses? It might if the committees had a defined suspicion of specific crimes that intersect its legislative interests. At the moment, all Congress has is a desire to rummage through the Trump family ledgers. No one has proposed any specific crime yet, let alone any legislative interest other than prurience.

Perhaps a court will give Congress the benefit of the doubt here, but this sets up a very uncomfortable precedent. Can any future Congress use their subpoena power to expose the business records of presidential contenders from the opposite party in the future? Wouldn’t the civic-hygiene argument work whether or not that candidate was an incumbent? In fact, it seems more than likely that Democrats would have tried this in 2016 after Trump refused to release his tax returns if (a) they had the majority and (b) they thought they could have gotten away with it.

If the courts allow these subpoenas to stand over private business records regardless of any clear legislative interest not connected to the next election, these subpoenas will become a regular feature of American presidential elections. That would put Congress in position to “qualify” candidates for the executive branch in a manner that distorts the separation-of-powers doctrine in the Constitution. It’s an argument worth making, at least, and one that the Supreme Court will end up settling.

That’ll take a long time, of course, which plays well for both sides. Under normal circumstances, fighting subpoenas is a bad look for an incumbent president, but these are not normal circumstances. After the collapse of the Russia-collusion narrative, Democrats run a serious risk of overplaying their hand with attacks on Trump’s businesses and family. This may look a lot less like presidential prevaricating outside the Beltway bubble, and a lot more like Democratic sour grapes.