It’s beyond redundant to say that Donald Trump must be impeached over the Ukraine scandal. The so-called transcript of his July phone call with Ukrainian President Volodymyr Zelevsky released last week — really a collection of notes — was already damning evidence of the president manipulating foreign policy for his personal political goals. Then the actual whistleblower complaint reconfirmed and solidified the case. Trump’s White House counsel, Donald McGahn, even wrote a memo cautioning him that using law enforcement powers to target a political adversary would be illegal and clearly impeachable.

But if Democrats are going to uncover more information through aggressive hearings and ultimately impeach the president, they need to recognize their most powerful adversary: Attorney General William Barr.

Barr has not just failed in his duty to carry out and enforce the law as attorney general. He has also used the power of his office to go after Trump’s enemies. We now know that he has served as a leading “diplomat” for a sort of shadow “the president is the state” foreign policy, conducted with at least the United Kingdom, Italy, and Australia. Barr is a leader in a broad administration effort to demand that U.S. allies aide Trump in legitimizing, maintaining and strengthening his personal hold on power.

Barr, in other words, is a key target of any investigation into Trump’s seemingly criminal abuse of power. This gives Democrats ample justification to zero in on the attorney general.

Not to mention that Barr’s ongoing refusal to recuse himself from the investigation into the whistleblower complaint. This is mind-bogglingly indefensible. Barr is managing to behave even less ethically than his horrific predecessor, Jeff Sessions.

But Barr’s misuse of his office well precedes these newest revelations. His Justice Department greenlit an indictment of former acting FBI Director Andrew McCabe, even summoning back a grand jury after months of hiatus. McCabe’s alleged crime? Letting agents talk to a reporter. This supposed wrongdoing is so flimsy, and the case surrounding it so like a banana republic, that it’s even prompted McCabe’s legal team to build a legal defense around Barr’s clear double-standard regarding whether a news story is helpful or harmful to Trump.

Barr had already launched an inquiry into the “origins” of the Russia investigation, a clear effort at whistleblower intimidation. He even opened an antitrust inquiry into major auto dealers just because they embarrassed Trump on an environmental deregulation.

With respect to the whistleblower case, Barr initially refused to turn over evidence central to the Ukraine case. Why? The Trump administration claimed that a dubious legal decision from Barr’s Office of Legal Counsel said they didn’t need to. Pretty convenient, since Barr has long fought to constrict access to White House information. But the relevant whistleblower law is clear; the executive branch must cooperate and turn over the evidence. It just refused to do so. That’s illegal.

Of course, this wasn’t Barr’s first go-round at stonewalling the public on information about Trump’s criminal dealings with a foreign power. The “Barr Letter,” as it’s now known, was infuriatingly successful at framing the narrative around the Mueller Report before the press or public had read a word of it. His actions since have been no less groveling. He even booked a holiday party at the Trump International Hotel in Washington, shoving some money back to his boss in another sign of deference.

Any attorney general is supposed to work to enact the president’s agenda. But Barr’s devotion is to Trump himself, rather than the office of the presidency and ideals or goals of the executive branch. Don’t forget that during the Nixon impeachment, the Saturday Night Massacre—the October 1973 event that began to turn public opinion firmly against Nixon—centered squarely on whether an attorney general would serve the president or the presidency. Nixon’s handpicked attorney general — Richard Nixon’s! — and deputy attorney general had the integrity to resign rather than abuse their office. Barr has, instead, shown he relishes serving as Trump’s “Roy Cohn.” That’s dereliction of duty, and the remedy is impeachment.

Turning the spotlight on Barr might restrain some of his efforts to safeguard his boss, especially as Barr tries to protect his imagined post-Trump career (or simply to avoid prison, should Trump fail to pardon him). Barr scrambled to say that he had no idea Trump mentioned him on the phone call when the story initially broke. That argument has gotten more and more tenuous as more and more details about Barr’s personal involvement in Trump’s political deals with foreign leaders have come to light. If Democrats push hard, they might get Barr to recuse himself. Besides the man himself, voicing a clear critique of the Trump Justice Department might encourage (or frighten) some other Justice staffers to turn whistleblower, along the lines of their counterparts within the intelligence community and IRS.

Moreover, impeaching Barr would just be good tactics for Democrats seeking to preserve and protect other investigations. Keep in mind that just this week Barr’s U.S. Attorney in the Southern District of New York has sought to block the Manhattan DA from accessing Trump’s tax returns as part of a local criminal investigation. How many less obvious ways is Barr running interference for Trump’s personal legal interests?

Just as with the president, impeaching Barr in the House would not remove him from office, but would shift the focus to a trial in the Senate. It would mean that each new revelation of Barr’s thuggery would play out against a backdrop of a pending impeachment vote and trial. And just as with this president, even if Barr is ultimately acquitted, forcing Republican senators to go on the record defending obviously criminal activities conducted by the highest law enforcement official in the land would be both good politics and the just, moral thing to do.

Recall that neither Nixon nor Bill Clinton were ultimately convicted in the Senate, but their impeachments are the first things we recall about each of them. If impeachment is about telling the public a story about why they cannot trust the current president, that story would be incomplete in Trump’s case without showing how his Cabinet, advisers, and confidants have engaged in the same profiteering and corrosion of the executive branch’s integrity as their boss. It’s not just one bad apple, it’s an entire culture of rot. Barr is the perfect surrogate for this part of the story, both for tactical and narrative reasons.

For nine months, Democratic leadership ho-hummed about the national need for impeachment. They only, finally, changed course when the pressure from activists and primary challengers became too much to bear. Now Democrats need to carry the momentum and prove to the public that they aren’t treating this as a stunt or a game. That means they can’t kowtow the minute Trump inevitably tries to obstruct them, almost certainly through Barr. The path to a serious inquiry is clear. To impeach Trump, impeach Barr.