Because this power [of investigation] is “justified solely as an adjunct to the legislative process,” it is subject to several limitations. Most importantly, a congressional subpoena is valid only if it is “related to, and in furtherance of, a legitimate task of the Congress.” The subpoena must serve a “valid legislative purpose,” Quinn v. United States, 349 U.S. 155, 161 (1955); it must “concern[ ] a subject on which legislation ‘could be had,’” Eastland v. United States Servicemen’s Fund, 421 U.S. 491, 506 (1975) (quoting McGrain, 273 U. S., at 177).
Furthermore, Congress may not issue a subpoena for the purpose of “law enforcement,” because “those powers are assigned under our Constitution to the Executive and the Judiciary.” Quinn, 349 U. S., at 161. Thus Congress may not use subpoenas to “try” someone “before [a] committee for any crime or wrongdoing.” McGrain, 273 U. S., at 179. Congress has no “‘general’ power to inquire into private affairs and compel disclosures,” id., at 173–174, and “there is no congressional power to expose for the sake of exposure,” Watkins, 354 U. S., at 200. “Investigations conducted solely for the personal aggrandizement of the investigators or to ‘punish’ those investigated are indefensible.” Id., at 187.