In July 2016, during the presidential campaign, when Comey publicly announced that Hillary Clinton should not be prosecuted for her email peccadilloes — but strongly criticized her behavior in setting up a private email server while in her role as US secretary of state—Trump did not complain that Department of Justice (DOJ) norms were being violated. He did not object to the FBI Director usurping the prerogative of DOJ lawyers to decide whether or not to file criminal charges, or to the FBI Director discussing a criminal probe involving a candidate during election season. Instead, Trump complained that Comey had not gone far enough. Trump was upset that Comey had not demanded that Clinton, his electoral rival, be indicted. “Lock her up!” was chanted at Trump rallies.

Then, in late October when Comey issued his extraordinary letter about re-opening the Clinton investigation on the eve of the election, Trump and Sessions, then an important Trump supporter campaign surrogate, were jubilant and full of praise for Comey.

But on Tuesday, Sessions and Trump told America that they were so disturbed by Comey’s violations of DOJ policies and norms concerning the Clinton matter that they concluded he must be fired.

There is no reason to believe that Trump and Sessions had a good faith change of heart. It is simply not credible that solicitude for Hillary Clinton’s treatment by the FBI drove this decision.

If not the stated reason, what else might explain the firing of this FBI director, at this time?

Comey has shown that he will stand up to presidents, attorneys general, and presidential candidates. He won fame and bipartisan respect during the George W. Bush administration when, as Deputy Attorney General, he threatened to resign rather than agree to re-authorize the illegal warrantless wiretapping program. Because he perceived that her independence was compromised by a private talk with Bill Clinton, Comey nudged aside Obama’s Attorney General Loretta Lynch to make the call about not prosecuting Hillary. And he again took the lead to report that the FBI had re-opened the investigation in late October. In March of this year, Comey publicly testified that there was no evidence for Trump’s baseless claim that President Obama had personally ordered the wiretapping of Trump Tower. On top of this rebuke, he further testified that there was an ongoing FBI counter-intelligence investigation about collusion between the Trump campaign and Russia’s disturbingly successful email hacking and election manipulation scheme.

Trump, his administration, and his congressional allies were terrified about what an independent FBI investigation would uncover. They were terrified what an FBI Director of demonstrated independence would do and say. They were terrified that Comey might once again usurp DOJ prerogatives about deciding on criminal charges by making public his views about who should be indicted. Michael Flynn, perhaps? Paul Manafort?

Damaging leaks about Trump’s motives for the firing are coming fast and furious. CNN is reporting that this week the FBI sent grand jury subpoenas to associates of Flynn. Politico relays that President Trump has become so “enraged” by the Russia probe that he screams at the television when it is discussed. The New York Times reports that this week Comey met with the Deputy Attorney General—Rod Rosenstein, who is standing in for the recused Sessions on the Russia matter, and who wrote the memo justifying the Comey firing—to request a significant increase in personnel and resources for the Russia investigation. And the Times also reports that the White House was actively shopping for justifications for firing Comey. And voila, Sessions and his deputy Rosenstein produced the impossible-to-believe story that was released Tuesday.

In prior generations, Americans have experienced politicized federal law enforcement. Under J. Edgar Hoover, the FBI interfered in politics and spied on civil rights and anti-war activists. Richard Nixon deployed the powers of the state against real and perceived political enemies. But since Hoover died and Watergate was exposed in the early 1970s, major efforts have been made to reform the Bureau and DOJ to keep them from infringing civil liberties and intervening in politics.

The FBI Director has a 10-year term in office, specifically chosen to be lengthy and not tied to the presidential election cycle, in order to promote independence from politics. It is true that presidents are still legally entitled to fire the FBI director. And it is true that President Bill Clinton did so, but that occurred at the beginning of Clinton’s first term, because of documented financial improprieties by Director William Sessions that had been investigated during the George H.W. Bush administration.

By contrast, firing an FBI Director who is investigating the White House, for reasons that are transparently political and self-protective, is an outrageous breach of faith with the American people and with the Bureau itself. It has the potential to destroy generations of work by presidents, attorneys general, FBI directors, and Congress to keep politics out of law enforcement.

Comey’s firing is all the more disturbing because it comes on the heels of Trump’s firing of another law enforcement official whose demonstrated independence was a threat to Trump and his circle: Preet Bharara, the U.S. Attorney for the Southern District of New York, who had jurisdiction over events happening in Manhattan, where Trump Tower happens to be relocated. Trump initially asked the widely-respected Bharara, an Obama appointee, to stay on in the job but then abruptly fired him without explanation.

The rule of law and apolitical law enforcement are under attack by a president who is a walking conflict of interest, with his un-divested businesses, nepotistic hiring, and unprecedented lack of transparency about personal finances. This president rages on Twitter when courts have the temerity to rule against him and when journalists do their jobs by questioning him. This same president may well have been helped into office by a hostile foreign intelligence service colluding with his campaign. It is past time for Republicans leading Congress to wake up to the dangers that President Trump poses. Our free press and the courts can do their part. But the lesson of the Nixon years is that Congress is the only institution with sufficient power and constitutional resources to stand up to a president who flouts the rule of law. Until 2020 that is, when the American people will have their say.

Andrew Kent is a professor of law at Fordham University School of Law in New York City.