Andrew Koppelman is the John Paul Stevens Professor of Law, and Steven Lubet is the Williams Memorial Professor of Law at the Northwestern University Pritzker School of Law. The opinions expressed in this commentary are their own.

(CNN) Rep. Jason Chaffetz has some explaining to do. As chairman of the House Committee on Oversight and Government Reform, the Utah Republican spared no effort in leading the multiple investigations of Hillary Clinton. Yet he has shown little interest in investigating, or even questioning, President Donald Trump's myriad financial entanglements. His explanations of the difference suggest that Chaffetz doesn't even understand why Congress has the power to investigate in the first place.

In the month before the 2016 election, Chaffetz referred to a potential Clinton administration as a "target-rich environment," and he vowed to remain relentless following her loss. "The investigation continues," he tweeted on Inauguration Day. As it happened, that was also the day on which his investigatory zeal seemed to flag, at least regarding the current occupant of the White House.

"The Democrats can flail and complain and run around with their heads cut off," he said after meeting with Trump last week, but "the reality is he's exempt" from the federal conflicts of interest statute. That seemed to end the discussion for Chaffetz, disregarding the fact that the president is still covered by the Constitution's Emoluments Clause.

In any event, that was not good enough for some of the congressman's constituents. At a town hall meeting this week attended by more than 1,000 Utahans , Chaffetz heard repeated calls -- often accompanied by "clamorous boos" -- for an investigation into Trump's finances. He steadfastly declined, saying he had not seen any evidence Trump had used the presidency "to ingratiate his family." "You're not going to like this part," he told the frustrated crowd. "The president, under the law, is exempt from the conflict of interest laws."

Chaffetz was referring to the US Criminal Code , which makes it a crime for executive branch employees to participate in official decisions that might affect their personal financial interests. The president, however, is not an employee of the executive branch, and so that particular provision of the criminal law does not apply to him.

In Trump's words , "The law is totally on my side, meaning the president can't have a conflict of interest." That was not true, of course. The president can -- as a factual matter -- have financial interests that conflict or interfere with his obligations to the nation, even though he is not subject to the same penalties as other government officials.

And that is also where Chaffetz gets things completely wrong. The chairman of the House Oversight Committee seems to think his only duty is to investigate potential crimes. If the president can't go to jail, well, there is nothing to see here, and we can all move along. But the actual job of a legislative committee is to investigate the need for legislation, not the need for law enforcement. So the question for Chaffetz is not whether Trump is exempt from the law, but rather, whether the law itself should be changed.

As Republicans are fond of pointing out, our government is one of limited powers, all of which are spelled out in the Constitution. The powers of Congress are enumerated in Article I, which does not say anything about conducting investigations. Nonetheless, the US Supreme Court has consistently held that the power to make laws implies the power to conduct investigations. Thus, Congress can legitimately investigate any question "on which legislation could be had and would be materially aided by the information which the investigation was calculated to elicit."

As the court explained in Watkins v. United States (1957), the power of Congress to conduct investigations is inherent in the legislative process. That power is broad. It encompasses inquiries concerning the administration of existing laws as well as proposed or possibly needed statutes.

In other words, the function of an investigative committee is to act as the eyes and ears of Congress in obtaining facts upon which the full legislature can act, and that includes amending laws in light of changed circumstances.

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As was evident in Chaffetz's own deep-red district, millions of Americans -- and not only Democrats -- are worried about the effect that Trump's financial empire might have on his conduct in office.

The current conflict of interest laws have turned out to be inadequate to impose any restraints on the President -- including disclosure of the extent of his investments, or the identities of investors, from which countries, who may have leverage over him. But that is a good reason to open an investigation, not to foreclose one.

Congress needs to consider whether to change the law to fit the unprecedented Trump era, and the first step is to determine the nature, scope and details of the President's worldwide holdings.

Chaffetz attended Brigham Young University on a football scholarship, and he still holds several school records for kicking extra points. He was evidently a great placekicker, but on the important questions of Trump's financial conflicts of interest, he has regrettably chosen to punt. As the President himself might say: Sad!

Note: An earlier version of this story incorrectly said the powers of Congress are enumerated in Article II of the Constitution; they are in Article I.