Attorney General Jeff Sessions did not tell the truth in his sworn Senate confirmation hearing, and skirted the truth in the written questionnaire accompanying it.

The next steps, according to precedent and law, are clear: An FBI investigation must commence to determine if there are grounds to indict Sessions for perjury, and an independent prosecutor must be appointed to look into Sessions’s conduct in particular, and perhaps the Trump administration’s ties to Russia in general.

On Jan. 10, Sen. Al Franken cited then-newly released documents alleging high-level Trump campaign contacts with the Russian government. Franken said several times that these documents had not been verified, but then asked, “If there is any evidence that anyone affiliated with the Trump campaign communicated with the Russian government in the course of this campaign, what would you do?”

Sessions—who had sworn under oath to tell the truth at the start of his hearing—replied, “Sen. Franken, I’m not aware of any of those activities. I have been called a ‘surrogate’ at a time or two in that campaign, and I didn’t have communications with the Russians, and I’m unable to comment.”

In fact, as The Washington Post revealed Wednesday evening, Sessions did have at least two communications with Russian government figures, including what the Post described as “a private conversation between Sessions and Russian Ambassador Sergey Kislyak that took place in September in the senator’s office, at the height of what U.S. intelligence officials say was a Russian cyber campaign to upend the U.S. presidential race.”

Separately, as part of the written materials accompanying the confirmation process, Sessions was asked by Sen. Patrick Leahy, “Several of the president-elect’s nominees or senior advisers have Russian ties. Have you been in contact with anyone connected to any part of the Russian government about the 2016 election, either before or after Election Day?”

“No,” he replied.

Both statements are sufficiently close to perjury to warrant an immediate FBI investigation.

Federal law defines perjury as when an individual under oath “willfully and contrary to such oath states or subscribes any material matter which he does not believe to be true.”

Sessions’s case depends on the word “willfully.” Clearly, the statements were material; they are crucial matters of national security. It’s also clear that his response to Franken was inaccurate, and the accuracy of his response to Leahy hangs on the phrase “about the 2016 election,” since we don’t know what he and the Russian ambassador discussed.

Indeed, Sessions’s response to the new revelations is a tacit admission that he did communicate with Russian officials, just not about the campaign. “I never met with any Russian officials to discuss issues of the campaign. I have no idea what this allegation is about. It is false.”

“To discuss issues of the campaign,” maybe. But his Jan. 10 statement was far more general: “I didn’t have communications with the Russians.”

That’s clearly not true. But to be guilty of perjury, Sessions had to know that it was untrue.

That’s why the next step, in cases such as these, is an FBI investigation to determine what Sessions knew, when he knew it, what other contacts may have taken place, what Sessions and Kislyak discussed, and whether it is plausible that Sessions somehow did not remember his meetings with the Russian diplomat.

The normal procedure is for Congress to request an FBI investigation. Heretofore, House Oversight Committee Chairman Jason Chaffetz (R-UT) has declined to investigate a host of alarming allegations regarding Russian contacts with the Trump administration—but this may be different.

Interestingly, when Chaffetz was investigating Hillary Clinton’s email server—how quaint those misdeeds seem now—he scolded FBI Director James Comey for not launching an investigation on his own instead of waiting for a request from Congress. In other words, the FBI need not wait.

Nor should it. Sessions made a clearly false statement under oath. Is it perjury? That’s for a court to decide. But is it worthy of investigation? Of course.

Compare that to Clinton, who may or may not have lied when she said she didn’t recall any emails marked as classified on her personal account. For that to be perjury, she would have to have seen the emails marked “C,” known what the marking meant, remembered seeing them, and deliberately lied about it. And yet that merited a full FBI investigation that may have swung the presidential election.

Normally, the next step is for the FBI to issue a report, including a recommendation to indict or not to indict, which the Justice Department takes under advisement. In this case, however, it would be absurd for the FBI to tell Sessions to indict himself. Legally, it’s a conflict of interest. Practically speaking, it’s ridiculous.

Already, the White House is in denial mode, calling the reports “the latest attack against the Trump administration by partisan Democrats.” Obviously, this administration cannot be expected to investigate itself when it is already denying there’s anything to investigate.

That, of course, is why special prosecutors are appointed, either by the Justice Department, by the president, or by Congress.

To be clear, the appointment of a special prosecutor and the launching of an FBI investigation are not equivalent to a guilty verdict. Maybe the FBI will find exculpatory evidence. Maybe the special prosecutor will determine that it’s impossible to prove that Sessions knew he wasn’t telling the truth. Like anyone else, Sessions deserves a fair investigation and, if charged, a fair trial.

But unlike anyone else, Jefferson Sessions is the attorney general of the United States. Surely, as a lawyer with a long and distinguished record, he must recognize the obvious conflict of interest to have his colleagues and subordinates investigating his own activities.

Really, the only remaining question should be the scope of the special prosecutor’s mandate. That scope could be quite narrow, confined to Sessions’s own conduct and statements. But it should be broader. Now that we know that Sessions has misrepresented (willfully or not) his own contacts with Russia, we know that the administration’s contacts are wider than we thought. We also know that Sessions himself is involved.

As a result, it makes sense to launch a single investigation, rather than appoint a prosecutor with a narrow mandate, only to have to go back and either appoint another one or expand the mandate later. The special prosecutor’s office needs a robust mandate to follow the truth where it leads. This is not strictly required by the new Sessions revelations, but it is obviously the most logical—if not the most politically palatable—course of action.

It is also the most patriotic. The stakes could not be higher.