Special counsel Robert Mueller seems to be zeroing in on the question of whether President Donald Trump obstructed justice.

But not all experts agree that the public evidence alone is enough to make clear he has a strong case.

“This is not yet the type of case we’d ordinarily see an [obstruction of justice] indictment come out of,” Laurie Levenson, a former prosecutor and law professor at Loyola University, told me.

Levenson emphasizes that we don’t know the full of extent of what Mueller might have. If we limit ourselves to what’s publicly known, though, she said: “It’s troubling conduct that warrants an investigation. But whether it’s clear enough on its face, I don’t know.”

That’s in contrast to other experts, who’ve been arguing that what we know already is enough to put Trump in serious legal jeopardy.

“If Trump exercises his power — even his lawful power — with a corrupt motive of interfering with an investigation, that’s obstruction,” Lisa Kern Griffin, an expert on criminal law at Duke University, recently told my colleague Zack Beauchamp. “The attempt is sufficient, and it seems to be a matter of public record already.”

Experts who disagree believe that Mueller would likely need much more damning evidence to justify making an obstruction case — through either an indictment or an impeachment referral — against Trump. They tend to make some combination of these three arguments:

1) The uniqueness of the president’s role creates a whole host of legal, constitutional, and political obstacles here.

2) Trump’s allegedly obstructive conduct doesn’t quite match the two presidential precedents we have here. The obstruction of justice impeachment articles Presidents Nixon and Clinton faced accused them of destroying or withholding evidence and telling witnesses to lie under oath.

3) Finally, Trump’s possible motive is more difficult to prove than many are acknowledging with the evidence we have so far. That’s because he can still make the case that rather than acting to cover up crimes, he acted because he genuinely believes the Russia investigation is “fake news” and that he did nothing wrong.

Again, it is of course possible that Mueller has, or will obtain, stronger evidence. “We don’t know what we don’t know,” Levenson said. But, she continued, “I don’t think they’re likely to ask the grand jury for charges [against Trump] unless they have a bulletproof case.”

The skeptics’ first argument: the president is special

Back in December, Trump lawyer John Dowd claimed that it was impossible for Trump to be guilty of obstruction of justice, simply because he’s the president — an assertion that was roundly derided by legal experts.

Those I interviewed thought it was quite a stretch to assert that the president can’t obstruct justice. Still, they said there are several elements of the president’s unique position that could complicate efforts to make an obstruction case against him.

For one, as president, Trump is “in charge of the administration of justice. He is the top executive officer, and law enforcement is an executive function,” Eugene Kontorovich, a law professor at Northwestern University, told me. The president is also the boss of the attorney general and FBI director and has the power to fire them.

And while the norms of recent decades have dictated that Justice should operate with a measure of independence from the president, it’s far from clear that those norms have the force of law. “Presidents used to be much more involved in matters that would directly affect them in ways that we would consider unethical today,” Kontorovich said. “Recent norms are just that: norms.”

As an example: Is it on its face illegal for the president to recommend the FBI be lenient toward an associate under investigation, as Trump allegedly did for Flynn? Kontorovich argues that it wouldn’t be — even if Trump knew Flynn was guilty. “No laws are enforced 100 percent. Lots of people commit crimes; lots of prosecutors know about them and decide not to charge those crimes,” he says. “Executive discretion and prioritization are part of the justice system.” And Trump is at the top of the justice system.

Other experts disagree. Jens David Ohlin, vice dean and law professor at Cornell University, told me that just because the president has a certain power, that “doesn’t mean that he can’t exercise that power corruptly.” As an example, he said that firing an employee “to interfere with an ongoing investigation” would be “an offense against the administration of justice.”

Still, there’s an even bigger problem: It’s not clear if prosecutors even can indict a sitting president. The Justice Department’s Office of Legal Counsel has long taken the position that they can’t. Some legal experts argue otherwise, and the matter has never been tested in court. Still, this means that any indictment of Trump would be legally dubious and enormously controversial — likely involving a Supreme Court battle.

For that reason, many observers have long thought that if Mueller and his boss, Deputy Attorney General Rod Rosenstein, conclude Trump committed illegal acts, they’ll likely submit a report on their conclusions to Congress — putting the ball in their court and letting them decide whether they think censure or impeachment is justified.

This would skirt the legal difficulties of relying on the federal obstruction of justice statute, because impeachment isn’t a legal process at all — it’s a political one. Yet in other ways, this would make Mueller’s task harder. The Republican-controlled Congress has an obvious partisan incentive to give Trump the benefit of the doubt on any accusation that’s less than rock-solid (and probably even some that are rock-solid).

The skeptics’ second argument: so far, Trump’s alleged acts aren’t as bad as Nixon and Clinton’s

So if Mueller’s endgame is going to Congress, he could well feel pressured to clear a higher bar, in terms of both evidence and precedent, than he might for an ordinary indictment.

There are just two precedents for impeaching a president over obstruction of justice that he can rely on: Richard Nixon and Bill Clinton.

Though Nixon resigned before he could be impeached, the House Judiciary Committee started the process by approving two impeachment articles against him, one of which focused on obstruction of justice. Clinton was impeached for perjury and obstruction of justice, but the Senate acquitted him. Both were accused of, among other things:

Urging witnesses to outright lie under oath to investigators

Concealing evidence from investigators, or destroying evidence

Trying to buy potential witnesses’ silence (in Clinton’s case, through job assistance)

If Trump was accused of anything like that, Kontorovich says, an obstruction case against him would be far stronger: “Destroying evidence is not part of the prosecutorial duty, nor is suborning witnesses to perjure themselves.” Either, he said, would be outright trying to get “a false outcome” in a law enforcement proceeding — and couldn’t be excused as trying to advise the Justice Department on how to do its job.

But so far, there’s no clear evidence Trump did any of those things. The potential obstruction case against the president, to the best of our knowledge, focuses instead on:

Various inappropriate-sounding behind-the-scenes requests Trump made to law enforcement officials about the Flynn investigation

FBI Director James Comey’s firing

And perhaps the misleading public statement about his son Don Jr’s meeting with a Russian lawyer that the president reportedly helped craft

This conduct doesn’t exactly match the witness-tampering and evidence-tampering allegations that formed the core of past obstruction of justice impeachment articles, which seemed on its face illegal.

“There’s a difference if he did those things: paying off witnesses, telling them to lie, hiding witnesses,” Levenson said. “Then I think you have a very clear case. It’s a less clear case when he’s sort of saying [to law enforcement officials], ‘here are my thoughts.’”

Griffin, for one, argues that Trump’s actions aren’t so different. “Associates of Nixon engaged in illegal acts to further Nixon’s interests, and Nixon then pursued a course of conduct designed to impede the investigation into those acts,” she told me. For Trump, she said, there’s “similar evidence of corrupt intent to obstruct an investigation.”

Still, it does seem that an obstruction case against Trump would be far easier for Mueller to make, both legally and politically, if evidence of tampering with witnesses or evidence emerged.

The skeptics’ third argument: proving Trump’s motive could be difficult

If Mueller were to be stuck with the evidence we already know of in trying to make an obstruction case, then, much would hinge on whether the special counsel could prove Trump’s motive was corrupt.

“Trump’s actions, tweets, and other public statements suggest that he had a corrupt motive to impede the Russia investigation in order to protect himself and his associates,” Griffin said.

Yet Trump’s line on the Russia probe — both in public and, to the best of our knowledge, in private — is quite different. He asserts that he thinks he’s done nothing wrong. His criticisms of the investigation, he said, are that he thinks it’s a “witch hunt” being used by his political and bureaucratic opponents to hurt his presidency.

Naturally, his claims here should be viewed with a good deal of skepticism. But that doesn’t mean there’s sufficient evidence to disprove them.

For instance, last May, Trump did contradict his aides’ story in a television interview, when he admitted the Russia probe was on his mind when he fired Comey. On its face, you might think that’s clear evidence of a corrupt motive.

But what the president specifically asserted went through his mind before the firing was that the Russia probe was a “made-up story” being used to benefit Democrats politically. That is, it’s consistent with a defense that Trump believed he did nothing wrong.

A further complication is that Comey has admitted he really did privately tell Trump that he wasn’t personally under investigation in the Russia probe. Trump can therefore claim he fired the FBI director out of aggravation with his public comments about an investigation he genuinely believed — and had privately been told — wasn’t about him.

As for Trump’s leniency request for Flynn, Kontorovich said, “People say that he did it because he was afraid of further prosecution and thought Flynn would flip on him. But that’s conjectural.”

Now, Griffin cites the fact that Trump asked others to leave the room before talking to Comey about Flynn as evidence of his corrupt intent. And that’s not all.

“He initially attempted to justify Director Comey’s dismissal by referencing the Clinton investigation,” she said. “And he later told Russian officials in an Oval Office meeting that he had terminated Director Comey to relieve pressure on his administration.”

Levenson holds out another possibility: “Donald Trump might be one of the few people who could get away with saying, ‘I was just clueless.’”

Mueller may need more. But there are several ways he can get more.

If the skeptics are right, Mueller probably needs substantially more — and more damning — evidence than we currently know of to justify an obstruction of justice finding.

But again, Mueller has held his cards remarkably close to the vest throughout this investigation. He’s reportedly interviewed a plethora of administration officials — White House aides, intelligence officials, and law enforcement officials — on the topic of potential obstruction of justice. We don’t know the full extent of what he’s learned.

Then there’s Michael Flynn’s cooperation, which could be crucial. We have no idea what Flynn has told Mueller since he agreed to a plea deal nearly two months ago. But now, per the Post, Mueller seems keenly interested in questioning Trump about Flynn-related events. Perhaps Flynn knows more about why Trump may have been so keen to urge the FBI to back off from him, and told Mueller what he knows.

There was also an intriguing report from Michael Isikoff last year that, after Flynn was fired and while he was under investigation, the former national security adviser told friends that he’d gotten “a message from the president to stay strong.” We don’t know what, exactly, that message entailed — and whether it perhaps may have amounted to witness tampering. But Flynn knows.

Another possibility, Levenson suggested, is that this has really been just a prelude to Trump’s expected interview with Mueller’s team. “Put aside obstruction. The easiest charge in the world, much easier than obstruction, is false statements,” she said. “So this next step — taking Donald Trump’s statements — is going to be very important.”

Finally, Mueller could also bolster an obstruction finding’s legal and political fortunes if he finds evidence of an underlying crime — especially evidence connecting Trump to Russian interference in the 2016 election. If it happened, this would provide stronger evidence of Trump’s corrupt intent — that he was acting to cover up criminal acts — as well as making the whole investigation tougher to dismiss politically.

In the end, whether Mueller pursues charges or a report to Congress, he’s surely well aware that doing either against a sitting president would be a monumental act. He and Rosenstein will be under enormous pressure to ensure their recommendations are firmly grounded in law and precedent, or they’d reap the political whirlwind. A thin case wouldn’t fly. The question is really whether they can make an unimpeachable one.