William Barr has a distinguished résumé: Aside from being one of America’s top lawyers, he has twice served as attorney general, first for George H.W. Bush and now for Donald Trump. But Barr deserves to be known for only one thing: his skill at shielding presidents from democratic accountability. During the Bush years, he spearheaded the successful effort to save his boss and Ronald Reagan from being implicated in the Iran/Contra scandal. When he shot down an attempt to set up a special counsel to investigate the Bush administration’s dealings in Iraq prior to the invasion of Kuwait, conservative columnist William Safire referred to Barr as “the Coverup-General.”

It was for his skill as Cover-up General that Barr was returned to his old post. As Democratic Senator Chris Murphy told The New Yorker, “I think he was nominated for his ability to protect Trump. His belief in executive power was his primary qualification.”

Barr has served Trump well. Writing in The Atlantic, George Packer observes, “Barr has used his authority to protect Trump from two investigations: that of Special Counsel Robert Mueller, and then the House impeachment inquiry. He hatched his own investigation to discredit the first, personally traveling abroad to dig up evidence of a United States government conspiracy against the president.”

Acting more as Trump’s protective consigliere than as the guardian of the legal system, Barr has gone after such perceived Trump enemies as former acting FBI director Andrew McCabe while offering aid to Trump friends like Roger Stone and Michael Flynn.

On Wednesday morning, two Justice Department employees are scheduled to testify before the House Judiciary Committee on Barr’s corruption of his office. Prosecutor Aaron S.J. Zelinsky will testify that political pressure was applied to give Roger Stone a lighter sentence than he would otherwise receive. John W. Elias, a senior career official in the antitrust division, is expected to talk about Barr pressuring his department to go after the legal marijuana industry and to sabotage efforts by the State of California to regulate automobile pollution.

Zelinsky’s prepared opening statements have already been made public. Zelinsky plans to tell the Judiciary Committee:

What I heard—repeatedly—was that Roger Stone was being treated differently from any other defendant because of his relationship to the President. I was told that the Acting U.S. Attorney for the District of Columbia, Timothy Shea, was receiving heavy pressure from the highest levels of the Department of Justice to cut Stone a break, and that the U.S. Attorney’s sentencing instructions to us were based on political considerations. I was also told that the acting U.S. Attorney was giving Stone such unprecedentedly favorable treatment because he was “afraid of the President.”

The Trump administration will try to dismiss Zelinsky’s testimony as hearsay. And it is true that, as Zelinsky himself says, he “was not privy to discussions with political leadership at the Department of Justice.” Still, Zelinsky oversaw the Stone case and his testimony about the pressures he felt are important. They fit in with a larger and known pattern of misconduct.

The sad truth about Bill Barr’s career is that it proves cover-ups usually work. Barr was part of the generation of young Republicans whose political sensibility was formed by Watergate. But the lesson they learned was not that presidential power should be restrained. Rather, Barr belonged to the school of Dick Cheney, Antonin Scalia, and David Addington. This cohort of Republicans all concluded that what Watergate proved was that presidential power, at least when Republicans held the White House, needed to be more securely guarded by legal loyalists.

These advocates of “the unitary executive” (as they call it) have won some singular successes—in part because the culture of elite impunity has bipartisan support. Iran/Contra was a great success: Not only were two presidents shielded from consequences, but many underlings were pardoned. Barr was the adviser when George H.W. Bush pardoned a clutch of administration officials on Christmas Eve 1992. In issuing these pardons, Bush attacked what he called “the criminalization of policy differences,” and said these issues should be settled by “the voting booth, not the courtroom.”

It’s a testament to the success of Barr and other Republican advocates of an imperial presidency that leading Democrats have bought into this idea. When Eric Holder was nominated to be attorney general under Barack Obama, he was asked about possible investigations into officials in the George W. Bush administration responsible for spying on US citizens, and approving or ordering the use of torture. Holder said, “We don’t want to criminalize policy differences that may exist between the outgoing administration.” Obama himself echoed these sentiments, saying, “We need to look forward as opposed to looking backwards.” By 2012, Holder had closed the investigations into torture without any charges ever being brought.

It’s still an open question whether Barr will face any thorough investigation into his corruption of the Department of Justice. Judiciary Committee Chair Jerrold Nadler has already ruled out the impeachment of Barr as a “waste of time.” The current hearings may generate some momentary drama—but they will soon be swamped by election news.

Democrats face a bind with Barr. There is a narrowly pragmatic case for adopting Obama’s “look forward” stance if Joe Biden wins the presidency. Biden will have his hands full dealing with issues like the pandemic, the economic meltdown, and the police violence. There’s little electoral advantage to going after the members of a previous administration. It would revive partisan anger and open Biden to the charge of being petty and vindictive.

Despite these pragmatic arguments, the “look forward” approach has clearly failed. Applying it to the crimes of Trump and his enablers would endanger American democracy. The four decades since Watergate have seen an intensification of corruption thanks to the system of elite impunity that protects both parties. The Trump administration is merely the lowest point so far of a downward cycle.

But there is always lower to go. If there is no punishment, corruption will inevitably get worse. Trump has created a road map for future authoritarian governments, showing how much an American president can do, providing his own party controls the Senate and he appoints a pliable attorney general.

The only way to break this descent into authoritarianism is to hold Trump and his lackeys responsible. It is too late for impeachment, but it is not too late for the next Democratic administration to investigate what Barr did as attorney general. This investigation will be imperative for American democracy.