Two days before Initiative 71 legalized possession of marijuana in the District, Rep. Jason Chaffetz (R-Utah), chairman of the House Committee on Oversight and Government Reform, informed Mayor Muriel Bowser (D) that her decision to proceed with implementation and enforcement would be a “willful violation of the law.”

A Feb. 24 letter from Chaffetz and Rep. Mark Meadows (R-N.C.) contended that the language of a continuing resolution enacted by Congress in December barred the use of appropriated funds by the District to legalize marijuana, and they characterized the mayor’s actions as a violation of that bar.

By demanding details about District employees who either “participated in any way” or “declined to participate” in activities related to Initiative 71, the letter reads more like a grand jury subpoena than a legislative inquiry.

Chaffetz is entitled to his opinion regarding the legality and wisdom of the mayor’s decision to move forward with marijuana legalization. As chairman of the House committee with jurisdiction over the District, he unquestionably possesses extensive legislative authority over D.C. operations. But that authority extends to writing laws regulating conduct within the District, not serving as a self-appointed sheriff; the Constitution demands that Congress leave enforcement to others. Congressional threats directed toward the mayor and written demands for information about District employees and operations overstep the bounds of Congress’s legislative power and threaten the viability of any legitimate legal inquiry into this process.

The constitutional boundaries of congressional power are well established: Chaffetz’s committee may act only to further a legislative purpose. This boundary applies even when the committee is exercising its extensive investigatory authority. As the Supreme Court noted nearly 60 years ago, Congress is not “a law enforcement or trial agency. These are functions of the executive and judicial departments of government. . . . Investigations conducted solely for the personal aggrandizement of the investigators or to ‘punish’ those investigated are indefensible.”

Chaffetz provided no legislative rationale for his demand for documents relating to the District’s implementation of the initiative. His letter clearly indicates that he considers the ban on implementation a settled matter that requires no additional legislative action. As such, it is hard to imagine how demanding details about employee activities — never mind stating that the mayor may have violated the law — could further congressional rulemaking efforts.

Consequently, Bowser may ignore the requests for documents and information. If she does, Congress could have a hard time effectively enforcing its demands through a judicial civil or criminal contempt process that demands a valid legislative purpose for such action.

Ironically, Chaffetz’s statements could undermine any legitimate legal inquiry into Bowser’s actions undertaken by appropriate law enforcement authorities. Federal courts have long recognized that congressional committees that generate publicity by investigating the subject matter of pending investigations or seek to influence legal inquiries can irreparably taint or invalidate those prosecutions.

One can understand why Chaffetz would be miffed about Bowser’s decision to proceed. But threatening letters on congressional letterhead will simply not cut it. The chairman would be far better served finding District residents who oppose legalization and encouraging them to sue the D.C. government to stop implementation. Until that time, Chaffetz, a former college placekicker, will probably find his efforts opposing the mayor’s action sailing wide right.

The writer is a lawyer with Miller & Chevalier and practices in the areas of civil and criminal federal litigation with a focus on federal campaign and election law and congressional ethics and investigations.