It's worth looking at the already strong publicly available evidence, as well as the supposed flaws in that case. Even taking into account possible shortcomings, the current case for an obstruction of justice charge is crystal clear.

Looking at it from the perspective of a prosecutor or a law school class, the three basic legal elements of obstruction of justice are satisfied in this case. First, Trump's alleged directive to his former FBI director would qualify as an effort to interfere with an investigation. Federal courts have said that virtually any act can create such liability for obstruction and that the act need not, by itself, be unlawful or even nefarious.

As long as the suspect has a specific potential proceeding in mind—any possible prosecution of Flynn would do here—this requirement is satisfied .

It's important to note that the relevant criminal statute prohibits obstruction of legal proceedings that might not yet be underway at the time of the offense but that could come to fruition—an investigation of Flynn was ongoing at that point, but there may not yet have been a grand jury.

Second, Trump's act allegedly was taken with a specific "official proceeding"—the potential prosecution of his former national security adviser—in mind as the object of the effort to obstruct.

Third, Trump's alleged actions clearly indicate a "corrupt" intent, which federal court rulings have said is a state of mind meaning "with an improper purpose to obstruct justice." There have been many federal cases in which efforts to derail or even slow a criminal investigation in order to protect associates were proven in court to meet this requirement. That is what apparently happened here.

There are other issues at play, of course. Some have argued that, elements of the crime aside, the president simply cannot be prosecuted for exercising his power to direct federal law enforcement priorities no matter how malevolent his intentions. This argument disturbingly equates the power to do something with the legality of exercising that power.

The Supreme Court has already acknowledged the inescapable logic that the president's authority over federal law enforcement does not include the freedom to prevent investigation and prosecution of himself and his close aides, as presidential powers expert Richard Pildes has explained. The opposing line of argument would excuse a parade of horribles including, hypothetically, a president who ordered his FBI director to mire an election opponent in a costly and distracting investigation for political reasons, or a president who ordered the halt to a murder investigation that might implicate a staff member.

A related claim is that the existence of the presidential pardon implies the power to snuff out any investigation at any stage. But no sensible rendition of the constitutional framers' intention could hold that their actual purpose was to grant the president a monarchical prerogative to ordain any legal outcome, on any subject, and at any time.

The principal defense to date from Trump and his advocates has been on the facts. They have denied much of the sequence of events laid out in Comey's testimony and in press accounts about his contemporaneous documentation of the meetings in question. Even assuming that this defense eventually points to specific contested facts and somehow resolves the president's own contradictory statements, the approach is going nowhere.

By the standards of federal criminal cases, Comey's credibility—on recall, detail, résumé, demeanor, bias, intelligence, contemporaneous documentation, and other standard witness metrics—is exceptionally strong. After watching Comey's testimony before the Senate Intelligence Committee, no experienced federal criminal lawyer, speaking candidly, would say otherwise. The chances of impactful cross-examination are minimal.

Comey's testimony also appears to be extensively corroborated. In addition to Comey's own writings, which would be admissible as evidence if Comey's credibility were attacked, President Trump allegedly made statements to others in the administration, to diplomats, and to the public that would bolster Comey's account.

A prosecutor would also attempt to corroborate innocent details in Comey's story as well as incriminating ones, including those that support the credibility of witnesses. For example, Comey's testimony that he spoke with Attorney General Jeff Sessions the day after his Oval Office meeting and asked not to be left alone with the president again was corroborated by Sessions himself.

Critically, the entire sequence of events—the alleged requests for "loyalty," the strange White House dinner, the handling of Comey's firing, the directive to Sessions and others to leave the Oval Office before the alleged Flynn request, even the president's dealings with others, such as the former U.S. attorney in Manhattan—fit together to portray a consistent and compelling story about the president's purpose in urging Comey to end the investigation of Flynn. Former FBI Director James Comey. Drew Angerer/Getty Images

Another implausible argument advanced on behalf of the president is that his alleged statements to Comey about dropping the Flynn investigation were not a directive because the president said only that he "hoped" Comey would act accordingly. (Trump denies saying even this.) As a matter of common sense, the argument that a person with immense power cannot mean to influence an underling when making a "mere" suggestion should strike anyone familiar with the milieu of The Sopranos as frivolous. As a matter of law, expressing "hope" can constitute obstruction of justice. The judicial decisions in obstruction of justice cases are replete with examples of people prosecuted for attempting to influence others subtly and through less than direct orders.

Yet another uninformed point has been made by some that Trump did not actually obstruct the Flynn investigation: Comey took no action, and even after Comey's firing, the matter goes on. There is probably no point on which the law of obstruction of justice is clearer: The crime consists of the effort to obstruct, not any actual obstruction. The obstruction statutes themselves include the words endeavor and attempt in their definitions of the offense.

In all the challenges to a potential obstruction case, there is only one issue of substance: whether the president can be proven to have acted with "corrupt" intent to obstruct justice when exercising his supervisory power over federal law enforcement personnel and their activities. Trump could try the novel argument that he lacked the "corrupt" mental state in his dealings with Comey because he believed himself to be exercising his lawful authority to control the enforcement of federal law.

The ultimate question is not whether President Trump thought he was legally allowed to cajole Comey about the Flynn investigation—ignorance of the law would be no excuse—but whether, when he did so, the president acted with a purpose that was "improper."

Clearing the room before he allegedly raised the Flynn matter with Comey is strong evidence the president knew what he was doing was "improper." It is also impossible to see how Trump's purpose here can be deemed "proper" without placing the president above the law. Even the president's keenest defenders must concede that attempting to stop the Flynn matter by offering a bribe to Comey or threatening his family, physically or economically, would have been improper. Former national security adviser Michael Flynn. Thomson Reuters

Trump's alleged actions were somewhat less flagrant here. But courts have ruled, for example, that an attorney can be charged with obstruction when engaging in conduct that would otherwise be ordinary and allowable for a lawyer—like filing lawsuits or giving advice to witnesses—if the lawyer does so for the purpose of protecting himself or his associates from prosecution. Similarly, if a president wields his normally legal executive power for the purpose of halting the investigation of himself or his associates, he acts with an "improper purpose" to obstruct justice.

Moving to the specifics of this case only makes this clearer. Although strong norms place authority over Department of Justice investigations in the attorney general's hands, a president might argue that he is entitled to order an investigation closed if he thinks it is a meritless waste of resources. But no evidence supports this as President Trump's motive in this matter. He himself has reportedly said otherwise. In any event, if a live investigation places the president at serious personal risk, legally or politically, it is impossible for him to exercise independent judgment on the merits of the matter.

A last line of defense might be to concede the argument for a legal case for obstruction but claim that no prosecutor would bring it. Individuals who come in contact with criminal investigations commonly engage in behavior intended to thwart the government, with lying being the most common such behavior. Prosecutors let the vast majority of this stuff go. President Donald Trump shakes hands with James Comey in the Blue Room of the White House on January 22, 2017 in Washington, DC. Andrew Harrer/Pool,Getty Images

This is different, though. Intervention in a potential criminal case against a former top government official by the highest of government officials falls well toward the serious end of the obstruction spectrum. The president, who swears a constitutional oath to "take Care that the Laws be faithfully executed," should be held to the highest standard where it comes to interference with justice.