After the days of mayhem that followed the firing of FBI Director James Comey last week, the biggest question now seems to be whom Donald Trump will pick as his successor. Will he nominate someone with a reputation as a consummate professional like Andrew McCabe, Comey’s erstwhile deputy? Or will he give the nod to a political loyalist like John Cornyn, the Republican senator from Texas?

If Trump nominates a political hack to replace Comey, the warning bells that political scientists have long been sounding about Trump would amp up to deafening levels. As Princeton political scientist Jan-Werner Müller explains in What Is Populism?, the first move taken by authoritarian populists who have successfully weakened democracy in countries like Poland and Hungary in recent years has been “to colonize or ‘occupy’ the state” by appointing their own cronies to head independent institutions: They have created new institutions they control. They have changed the rules governing existing institutions to bring them under the sway of the government. They have lowered the mandatory retirement age for civil servants to create vacancies. And, yes, where they could, they have fired politically inconvenient bureaucrats for spurious reasons.

If Trump hand-picks a docile FBI director who is likely to derail investigations against him, this would constitute a clear sign that he is starting to follow in their footsteps. At that point, anybody who votes for the nominee would rightly be remembered as a traitor to the republic for as long (or short) as the Constitution shall endure.

But while it would be outrageous if Trump nominates an obvious crony to head the FBI, I am not sure that the alternative is nearly as reassuring as many commentators seem to believe. Given the circumstances of Comey’s dismissal and the process governing his replacement, no successor picked by Trump can be trusted to oversee an investigation into Trump. That is why the only way to limit the immense damage that Comey’s firing has already done to basic democratic norms is to appoint an independent committee or special prosecutor with robust powers and a wide ambit.

When we look beyond the garish details over which we have obsessed for the past week and focus on the big, sordid picture, four especially concerning facts stand out.

1. Trump removed Comey because the FBI would not drop its investigation into his campaign’s links with Russia.

Some of the halfway competent people around Trump seemed to recognize the importance of concealing their boss’s true motives, so they asked Deputy Attorney General Rod Rosenstein to draft a spurious justification for firing Comey, and spent all of Wednesday denying the obvious connection to the Russia investigation.

But then Trump went in front of the television cameras and, with his peculiar candor, demolished the storyline his aides had assembled for him. He admitted that he had decided to fire Comey before consulting Rosenstein and that the Russia investigation was foremost in his thinking. “When I decided to just do it, I said to myself, I said you know, this Russia thing with Trump and Russia is a made up story, it’s an excuse by the Democrats for having lost an election that they should have won,” he told NBC’s Lester Holt.

As a result, the new FBI director will be well-aware of the fact that his or her job is only as secure as his or her pliancy is complete: If Trump was willing to dismiss one FBI director because he dared to pursue an investigation into malfeasance by the executive branch, there is no reason to think that Trump would be unwilling to dismiss another FBI director for continuing the investigation.

2. Trump abused his power to influence the director of the FBI.

Trump himself has bragged that he asked Comey whether he was under investigation by the FBI on three separate occasions, a clear breach of protocol. According to press reports, he also demanded a wholly inappropriate pledge of personal loyalty from Comey. Even after Comey had been fired, Trump didn’t let up, threatening the former director on Twitter and hinting at the existence of secret recordings to stop him from giving damaging testimony in front of Congress. All in all, the pattern of influence-peddling and witness-intimidation is undeniable.

Any successor to Comey must therefore know that the president is likely to interfere with his or her work in unconscionable ways: If Trump was willing to use his power to bend the work of one FBI director to his will, there is no reason to think that Trump would be unwilling to use his power to bend the work of another FBI director to his will.

3. The process for picking the next FBI director has already been corrupted.

Since the FBI is investigating Trump’s campaign, the president has a pressing reason to ensure that its new director will be friendly to him. The very fact that Trump will get to make the pick is thus a clear conflict of interest. And while the reasons why Trump can trust a particular pick to be loyal may be obvious in some cases, in other cases there may be less obvious reasons why he believes he can trust a person who appears reliable to the outside world. The one thing that is certain is that Trump is very unlikely to pick a candidate whom he truly believes to be impartial.

What’s more, Jeff Sessions was confirmed as attorney general after lying to Congress about his meeting with the Russian ambassador, an act for which he could potentially be criminally liable. And yet, he is now conducting interviews for the key candidates who would oversee the Russia investigation. This, too, is a clear conflict of interest and makes a mockery of his promise to recuse himself from that investigation.

In short, the people picking Comey’s successor are potential targets of serious investigations and have shown themselves willing to lie to Congress to further their own interests. It would be naïve to trust the person they ultimately appoint.

4. Even true professionals could be corrupted by Trump.

The brief and sordid tragedy of Rod Rosenstein shows that it would be equally naïve to assume that a pick who has, so far, always acted in a decent and professional manner would continue to act in a decent and professional manner after a few weeks on the job. When Rosenstein was nominated as Sessions’ deputy, Lawfare’s Benjamin Wittes, one of the most clear-sighted Trump critics, was “delighted.” Having known Rosenstein for many years, he had “always thought well of him” and “admired his ability to serve at senior levels in administrations of both parties and impress both sides with apolitical service.”

And yet, Wittes now recognizes that Rosenstein has become a stooge:

“Trump …used his deputy attorney general as window dressing on a pre-cooked political decision to shut down an investigation involving himself, a decision for which he needed the patina of a high-minded rationale. Once the President has said this about you—a law enforcement officer who works for him and who promised the Senate in confirmation hearings you would show independence—you have nothing left. These are the costs of working for Trump, and it took Rosenstein only two weeks to pay them.”

With his characteristic grace, Wittes admits that he had been “profoundly wrong about Rosenstein.” But the important thing now is to recognize why and how Wittes, and other Rosenstein backers, were wrong: Wittes seems to believe that a craven self-serving man has somehow managed to pass as a consummate professional for years. But I fear that the problem is much deeper and much more structural than that: To survive in the Trump administration, even consummate professionals will turn into craven self-serving men.

This, to me, is the most concerning lesson we should take from the past week: If Trump was able to corrupt Rosenstein so quickly and so thoroughly, there is no way to be sure that he won’t be able to corrupt a seemingly impeccable pick for FBI director as well. And if Trump is able to undermine the independence of the FBI and corrupt a widely respected man like Rod Rosenstein in a matter of months, we should worry that his administration can work the same poisonous effect on other institutions and civil servants in the next four years.

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What kind of investigation should Congress push for—a special prosecutor, a select committee, or an independent investigation? One thing is clear: Many of the proposals that have been made would be woefully insufficient. When people talk of a special prosecutor, for example, they are usually thinking of an independent official who is instituted by Congress and cannot be removed by the president. But the post-Watergate law giving Congress the authority to set up such a prosecutor expired in the late 1990s. Unless Congress passes a new law, which would require a veto-proof majority, a special prosecutor would therefore be far weaker than most people assume.

But one thing is clear: Whatever form the independent investigation of Trump’s activities takes, its ambit has to go well beyond the Trump–Russia nexus. At this point, there is good reason to believe that the FBI’s ability to investigate any wrongdoing by Trump or his associates has been significantly curtailed. To re-establish trust in our most vital institutions, we need to create a counterweight that is able to investigate potential wrongdoing in any corner of Trump’s universe.

Another, even more important thing, is just as clear: Any citizen who believes in the importance of the rule of law needs to ask their senator not to confirm any pick as FBI director until an independent institution has been set up to look into wrongdoing by Trump and his cronies. And any senator who votes to confirm Trump’s pick as the new director of the FBI before such an institution is set up is committing an act of great moral and political cowardice.