And more broadly, the Trump administration has been stonewalling congressional investigations from the get-go. After ignoring House subpoenas, the administration has refused to supply documents relating to the president’s tax returns and finances, Donald Trump and President Vladimir Putin’s private meetings, Michael Cohen’s payouts, and more. Within the weeks and months ahead, some of these fights will come before various courts with a question: Just how much oversight power does Congress have?

The potential significance of those cases is not limited to the current fight between this House and this president: The consequences of these court cases could far outlast this presidency, no matter how it ultimately ends. After all, congressional oversight is a critical component of the Constitution’s system of checks and balances, and if the courts accept the president’s arguments, they would strip Congress of one of the fundamental tools it uses to serve as an effective check on the executive branch.

Over the years, the Supreme Court has repeatedly approved of Congress’s exercise of its oversight authority, recognizing that Congress’s power to investigate is “broad,” encompassing “inquiries concerning the administration of existing laws, as well as proposed or possibly needed statutes,” and “surveys of defects in our social, economic or political system for the purpose of enabling the Congress to remedy them.” As the Court explained in 1927, a “legislative body cannot legislate wisely or effectively in the absence of information respecting the conditions which the legislation is intended to affect or change.” Thus, the Court said, “where the legislative body does not itself possess the requisite information—which not infrequently is true—recourse must be had to others who do possess it.”

In 1957 the Court made it clear that just as Congress has the power to investigate in order to determine whether and how to legislate, Congress also has the power to investigate when it is “related to, and in furtherance of” another “legitimate task of the Congress.” Thus, it follows that Congress can investigate when the results of the investigation could lead “to further action on the part of the [Congress] within its constitutional powers,” such as a decision to impeach.

Without this oversight power, Congress’s ability to fulfill its role in our constitutional system would be considerably hampered. For one thing, it would be less effective as a legislative body, deprived of the tools necessary to determine what its legislative priorities should be and how it can legislate most effectively. Indeed, while the oversight efforts that are making the headlines are the ones related to the White House, the House has already this year held nearly 200 hearings and sent more than 430 letters seeking information on a wide range of topics like emergency health care for veterans, abuse at skilled nursing facilities, natural disasters as a result of climate change, the impacts of trade policies on the U.S. economy, and the policies and priorities of the Food and Nutrition Service. In some of these cases, Congress is seeking information that will help it decide whether to pass new legislation; in others, it is trying to ascertain how legislation already passed is being implemented. Both of these are legitimate purposes, and oversight is necessary to both of them.

And now President Trump’s lawyers are doing their part, making arguments in court that, if accepted, would significantly limit Congress’s oversight authority going forward. Consider, for example, the arguments that the president’s lawyers have been making in cases involving the House’s efforts to obtain documents related to the president’s and his businesses’ finances. The House is seeking those records to determine whether and how to legislate on financial-disclosure requirements and presidential conflicts of interest, as well as on issues not specifically related to the president at all, such as lending practices, money laundering, and fraud at financial institutions. The White House has refused to comply and, stunningly, the Department of Justice has echoed the president’s tweets, arguing that a “congressional demand for the President’s personal records raises the specter that members of the Legislative Branch are impermissibly attempting to interfere with or harass the Head of the Executive Branch.” Its brief reads as if congressional oversight of the president should be viewed with great suspicion—rather than as an essential congressional tool, one that the Supreme Court has long and consistently recognized.

The president’s personal lawyers have argued, among many other things, that Congress lacks a valid legislative purpose because, in their view, Congress is actually seeking this information to engage in “law enforcement.” This, despite the fact that there is no law-enforcement action pending against the president—and there could not be given that Department of Justice guidance prevents one from being brought. (There is, of course, an impeachment investigation, but remember that Congress can engage in oversight in furtherance of its constitutional powers, including the power to impeach.) The fact that Congress might uncover crimes committed by the president or his associates does not invalidate an otherwise lawful investigation.

President Trump seems to think that the normal rules don’t apply to him—and his lawyers are asking the courts to change the normal rules that have long applied to congressional oversight to protect him. If the courts were to agree, the consequences wouldn’t be limited to the fights between this president and this Congress. Rather, they would do serious damage to Congress as an institution, hindering its ability to do its job and to serve as an effective check on the executive branch. And that, in turn, would do serious damage to the country.