James Comey will deliver bombshell testimony before the Senate Intelligence Committee on Thursday morning, that much is clear. He will present a disturbing and detailed account of his interactions with Donald Trump.

“I need loyalty, I expect loyalty,” Trump allegedly said to Comey, according to the former FBI director’s prepared remarks released on Wednesday.

Trump’s firing of Comey in May was suspicious for several reasons. Most obviously, it occurred against the backdrop of a looming federal investigation into the ties between Russia and Trump’s campaign, and even though Trump said at the time that he fired Comey over his handling of the investigation into Hillary Clinton’s emails, basically no one believes this, particularly because Trump himself undermined this argument days later in an interview with NBC’s Lester Holt.

Comey’s testimony is telling — not only did Trump demand “loyalty” and “honest loyalty” from Comey, but he also asked what the FBI director could do to “lift the cloud” of the investigation. But do Trump’s actions amount to obstruction of justice? And what does obstruction of justice mean in this context?

I asked six constitutional and criminal law experts to think through these questions.

“The [Michael] Flynn matter surely confirms that he wanted the investigation closed,” Joshua Dressler, a law professor at Ohio State University, told me after reading Comey’s prepared remarks. “But it remains ambiguous whether Trump ‘endeavored’ to impede the investigation,” which is necessary in order to meet the obstruction of justice threshold.

For Jimmy Gurulé, a law professor at the University of Notre Dame, Comey’s statements are more damning: “It is difficult to construe President Trump's statements on February 14 to former FBI Director Comey as anything other than a request to terminate the FBI investigation of Gen. Flynn for reasons other than the merits of the case. This is an attempt to endeavor and influence the due administration of justice under the federal obstruction of justice statute.”

Comey’s testimony will doubtless be just the beginning of discussions over whether Trump committed the crime that forced President Richard Nixon to resign.

Here’s what those experts said.

Defining obstruction of justice

Obstructing justice seems straightforward: an attempt to impede or undermine a criminal investigation. But there are some important caveats.

“It requires proof that the person corruptly or by threat influences, impedes, or endeavors to influence or impede the due administration of justice,” Dressler says. “It doesn't require proof that justice was obstructed — only that the person endeavored to influence or impede justice.”

In other words, one needn’t succeed at obstructing justice to be guilty of it. It’s enough to prove that someone deliberately sought to hinder an investigation. The problem is that intent is often difficult to prove, especially in a circumstance where there are multiple contradictory motives.

Mark Tushnet, who teaches constitutional law at Harvard, offered an even simpler definition: “doing something that corruptly interferes with an ongoing investigation ... or doing something that makes it harder for the prosecutor to prove that you committed a crime.” Corrupt intent means “specifically wanting to derail an investigation, to prevent it from reaching what otherwise would be its conclusion.”

It’s also worth remembering, according to Brandon Garrett, a law professor at the University of Virginia, that “there is a whole family of obstruction of justice statutes; it's not just one crime, and many of them overlap.”

“In general,” he continued, “obstruction of justice is broadly defined as corruptly influencing or impeding a federal proceedings.” What actually counts as a “federal proceeding” remains a matter of controversy, and one that bears heavily on this case.

We don’t yet know if there was a grand jury hearing concerning the Russia investigation. If there was, Trump almost certainly obstructed justice. If, however, there was only a FBI investigation, Garrett and others I spoke with agree it’s not clear that obstruction of justice charges are applicable.

But setting aside that dispute, the plainest legal definition of obstruction of justice is something like this: acting with the specific intent to interfere with a judicial proceeding.

How strong is the case that Trump obstructed justice based on what we already know?

There isn’t an easy answer to this question. Part of the reason is that we don’t have all the facts. But it’s also because of varying views on the powers of the executive.

Eric Posner, a professor of law at the University of Chicago, pointed out that if “the president is head of law enforcement in this country, and if the president is the head of law enforcement, then he has the authority to hire and fire and to tell his subordinates not to pursue certain investigations.”

But there are compelling counter-arguments to this: Gurulé, who also served as assistant attorney general for George H.W. Bush and undersecretary of the Treasury for enforcement under George W. Bush, insists that the constitutional right to hire and fire is not absolute.

“There’s no constitutional right to hire and fire that is without exception,” he told me.

Gurulé also sees at least three instances in which the president arguably violated obstruction of justice laws. The first is the actual firing of Comey. “If it’s clear that this was done with the aim of interfering with the investigation, that’s obstruction of justice.”

The second instance has to do with Trump’s conversations with Comey. “We know that the president asked Sessions and others to leave the room so that he could talk privately with Comey,” Gurulé says. “If the president urged Comey to back off Flynn, or even if he expressed his desire to see Flynn left alone, that strikes me as endeavoring to influence or obstruct the due administration of justice.”

Still, the question of intent remains. But if it’s true that this conversation occurred as reported and as Comey details, it would appear that the president wanted Comey to make a decision regarding the investigation based on something other than the merits of the case — and that’s obstructing justice by any reasonable standard.

The third potential instance of obstruction is Trump’s alleged conversation with Director of National Intelligence Dan Coats. According to the Washington Post, Trump asked Coats in March “if he could intervene with then-FBI Director James B. Comey to get the bureau to back off its focus on former national security adviser Michael Flynn in its Russia probe.” As with the Comey interactions, the whiff of obstructionism is strong here.

These are all discrete cases, Gurulé says, and they shouldn’t be conflated. Even if there’s a sound justification for Comey’s firing, “that doesn’t pertain at all to the conversation between Trump and Comey or between Trump and Coats.”

Particularly if the prospect of impeachment is in question, whether Trump committed obstruction of justice is relevant, but that doesn’t necessarily make it more or less likely to happen. Ultimately, as Christopher Slobogin, a professor of criminal law at Vanderbilt University, told me, “Congress gets to decide what constitutes a high crime and misdemeanor for impeachment purposes.”

Which is to say, even if Trump did obstruct justice, he will not be impeached unless a Republican-controlled Congress decides he ought to be.

What legal experts might look for in Comey’s testimony on Thursday

Some new facts may be revealed when Comey delivers not only his opening remarks but also his answers to questions from senators. Comey will also do a closed-door briefing following the public testimony. Legal experts were nearly unified in what they said they might be looking for.

Eric Posner was focused on “the reasons for Trump's firing of Comey and the relative weight he gave those reasons.” If Comey can speak to Trump’s intent, that will go a long way in determining whether justice was obstructed. Again, though, Posner cautioned: “We’ll probably learn that a whole host of factors drove Trump’s decision, and if so, it will be difficult to determine intent.”

The language Comey uses is critical for Christopher Slobogin. “If Trump merely said he ‘hoped’ the investigation would end, that might not be construed as impeding. If he said in the context of talking about the investigation that Comey should pledge loyalty to Trump, that would probably be impeding.”

It really matters, then, what Trump actually said to Comey. If Trump insisted that Flynn was a “good guy” who shouldn’t be harassed, that doesn’t meet the obstruction threshold. “Even if he wanted the investigation shut down or curtailed because he thought it was a waste of time,” Slobogin says, “it might not be improper.”

Comey has to confirm or at the very least suggest that Trump wanted to avoid discovery of misdeeds — by him or by his staff — in order to have obstructed justice.

Mark Tushnet echoed Slobogin’s answer. “Any indication of reasons that Trump gave for asking Comey to go easy on Flynn will be vitally important,” he told me. “The specific language is key. The reporting is that he said Flynn's a ‘good guy’ but you'd certainly need more than that to meet the obstruction of justice threshold.”

“I’m interested in how Comey characterizes the pressure that was placed on him,” Brandon Garrett said. “I want to know the intent behind that pressure. If it's true that he was pressured to drop the investigation, it's unlikely that was for arbitrary reasons.”

Thus, if Comey says definitively that Trump pressured him to drop the investigation, Trump will have a hard time proving that his intent wasn’t to “impede” or otherwise obstruct the process.

For Joshua Dressler, the bar was comparatively low. In his view, Comey need only affirm what’s already been circulated in the media: “If Comey merely stands by everything that's already been reported in the press and adds nothing else, that alone is enough to suggest pretty definitively that justice was obstructed.”