The recently-released memo from Attorney General Jeff Sessions indicating that he’s considering appointing a special counsel to investigate Hillary Clinton adds fuel to the fire of the newest grounds for impeachment hearings: pressuring law enforcement to investigate and prosecute specific political adversaries and others.

For decades, Republican and Democratic presidents alike have respected the independence of law enforcement. In 1940, Attorney General (later Supreme Court Justice) Robert Jackson warned that “the greatest danger of abuse of prosecuting power” was “picking the man”—or, in this case, woman—“ and then . . . putting investigators to work, to pin some offense on [her].”

But Trump did exactly that when he issued a remarkable series of public statements (including over Twitter) pressuring the U.S. Department of Justice to investigate “Crooked Hillary,” the Democratic Party, and other political adversaries. The issue is not whether Hillary Clinton, the Democratic Party, or Trump’s other laundry list of targets merit criminal investigation—the issue is that a chief executive who uses law enforcement to persecute political enemies is characteristic of a banana republic, not a constitutional republic.

In some cases, the justice system will resist this pressure. For example, in the military court-martial of Bowe Bergdahl for desertion, the defense cited Trump’s campaign statements calling him a “dirty rotten traitor” and suggesting that Bergdahl should be shot as evidence of unlawful command influence. The military judge was sufficiently concerned that he imposed a far lighter sentence (no prison time) than most expected.

But the mere fact that the president is attempting to pressure law enforcement to prosecute his political opponents is highly disturbing. As conservative columnist Jennifer Rubin observes, “[t]here is no president in modern memory who has repeatedly and directly called on the Justice Department to investigate a political opponent in such a manner.” The last president to try this was Richard Nixon, and it was the basis for an article of impeachment. Nixon tried to get the IRS as a weapon to investigate his political enemies (the IRS Commissioner refused), and used the FBI to wiretap reporters he deemed to be threats. This conduct was reflected in Congress’s proposed second article of impeachment against President Nixon:

2. He misused the Federal Bureau of Investigation, the Secret Service, and other executive personnel, in violation or disregard of the constitutional rights of citizens, by directing or authorizing such agencies or personnel to conduct or continue electronic surveillance or other investigations for purposes unrelated to national security, the enforcement of laws, or any other lawful function of his office; he did direct, authorize, or permit the use of information obtained thereby for purposes unrelated to national security, the enforcement of laws, or any other lawful function of his office; and he did direct the concealment of certain records made by the Federal Bureau of Investigation of electronic surveillance.

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5. In disregard of the rule of law, he knowingly misused the executive power by interfering with agencies of the executive branch, including the Federal Bureau of Investigation, the Criminal Division, and the Office of Watergate Special Prosecution Force, of the Department of Justice, and the Central Intelligence Agency, in violation of his duty to take care that the laws be faithfully executed.

Building on that precedent, we have added a seventh ground for an impeachment investigation of President Trump:

7. directing or endeavoring to direct law enforcement, including the Department of Justice and the Federal Bureau of Investigation, to investigate and prosecute political adversaries and others, for improper purposes not justified by any lawful function of his office, thereby eroding the rule of law, undermining the independence of law enforcement from politics, and compromising the constitutional right to due process of law

We call upon the House Judiciary Committee to launch an impeachment investigation immediately. This does not, and should not, need to wait for Special Counsel Robert Mueller to complete his criminal investigation; this issue is likely outside the special counsel’s jurisdiction, and in any event Congress has its own institutional responsibilities and authorities. The president’s conduct is a grave abuse of presidential power and a threat to the rule of law, and demands immediate action by Congress.