We don’t know yet how Trumpgate will shake out, but one outcome is coming into view: a constitutional crisis. Sooner or later, we’re likely to have one.

The contours of constitutional crises vary from country to country, though all feature a breakdown of the normal functioning of government. In the American system, they usually involve circumstances that were not anticipated by the framers or fights over the Constitution’s separation and delegation of powers.

The trouble has come over issues like states rights ( part of what led to the Civil War), presidential succession (In 1841, John Tyler was the first vice-president to take over after the death of the president and Congress wanted him to be “Acting President”), and disputed presidential elections, especially the one held in 1876 between Samuel J. Tilden and Rutherford B. Hayes .

The best analogy to today’s madness is also the most recent—Watergate. In 1973, in what became known as the “Saturday Night Massacre,” President Nixon fired Attorney General Elliott Richardson and Deputy Attorney General William D. Ruckelshaus when they wouldn’t fire Archibald Cox, the Watergate special prosecutor.

The questions raised so far by Trumpgate are similar: How much power does the president have over the executive branch? Is it obstruction of justice if the president does it? Can the president be indicted?

As several former federal prosecutors confirmed this week, former FBI Director James Comey’s testimony on Thursday was a roadmap for special counsel Robert Mueller to follow as he builds an obstruction of justice case against President Trump. The two men, friends and former colleagues, view the law in similar terms. Mueller is unlikely to believe the word of an habitual liar over that of a Boy Scout. It’s unlikely that juries will, either.

One key fact—as Comey stressed— is that Trump told Attorney General Jeff Sessions, senior adviser Jared Kushner and others to leave the Oval Office so that he could be alone with Comey to tell him to stop the investigation of former national security adviser Michael Flynn. This intentionality is harmful to “the newbie defense”—that Trump was new to the presidency and didn’t know that what he was doing was wrong—offered by House Speaker Paul Ryan and others. Ignorance of the law is no defense, anyway.

All of the other arguments from Trump apologists have also collapsed. According to former prosecutors, Trump’s use of “I hope” instead of “I order you” to stop the Flynn probe won’t get him off. "If you say, 'Nice storefront you have here. Pity if something should happen to it,' that doesn't help you when you burn down the store," says Michael Waldman, president of the Brennan Center for Justice. Neither would Comey's "leaking" (a classic Trump diversion) or the fact that he didn’t immediately report the crime, which ignores an FBI director’s well-established obligation not to do anything to impede his own investigation.

The best thing Trump may have going for him legally is his shamelessness. His seemingly dumbest moves—like telling NBC’s Lester Holt that he fired Comey over Russia and saying publicly that Flynn had suffered enough—seem at first to be important confessional evidence in the obstruction case. But they might offer him a measure of perverse protection. If smoking guns aren’t dramatic revelations, just casual props in a high stakes reality show, are they really so dangerous to him?

In line with this devil-may-care strategy, Trump switched on Friday to a constitutional argument. He retweeted the position of Harvard Law Professor Alan Dershowitz (apparently auditioning for the role of Trump’s impeachment attorney) that even if Comey is telling the truth, Trump didn’t do anything criminal because under the Constitution he has total power over the executive branch. Dershowitz argues that all Justice Department investigations are thus legally subject to the president's whims. So Trump's new message is: Move along, nothing to see here. He tweeted that Mueller had “no plausible case” and “we must distinguish crimes from pol sins.”

By coincidence, the American Constitution Society, an organization of progressive constitutional lawyers, was meeting in Washington this week. When I wandered by, I didn’t find much support for the Dershowitz/ Trump view, which Waldman compares to claiming that owning a car gives you the right to make it a getaway car. If I’d gone to a meeting of the comparable conservative legal group, the Federalist Society, I’d have likely heard the opposite. One party’s obstruction of justice is another’s presidential prerogative.

So now we will face a new tribal partisan split, this time not over health care or immigration but deep questions of law, accountability and constitutional process.

Soon we may be arguing over whether the president has the right to fire the special counsel. Odds are he’ll do so should Mueller recommend indicting him for obstruction of justice. Trump’s bad experience firing Comey wouldn’t inhibit him from repeating the move if his presidency and jail time are on the line.

Of course if Mueller finds hard evidence of collusion with Russians or financial improprieties by the Trump Organization (or both in the same scuzzy transaction, as seems plausible), it would be harder for Trump to fire him.

Another possible source of constitutional crisis: The idea that the president cannot be indicted and tried while still in office is widely assumed to be settled law but it isn’t.

Article I, Section 3 of the Constitution includes a long tangled paragraph about impeachment that has never been clarified by the Supreme Court. President Clinton’s lawyers argued in 1998 that it offers temporary immunity to the president until impeachment has been resolved by the House (which indicts) and the Senate (which acquits or convicts). This view was endorsed at the time by conservative legal scholars, including Jay Bybee, now a federal judge. But many other legal scholars say the Constitution neither states nor implies that indictment and trial cannot proceed at the same time as impeachment.

Some conservatives even argue that Article II, Section 2 gives the president the power to pardon himself, something else that Trump would not hesitate to do to save his skin. He'd probably pardon Flynn while he was at it, though he might also do so earlier, to keep him from testifying against him.

In June of 1974, two months before Nixon resigned, the Watergate grand jury declared the president an “unindicted co-conspirator.” He wasn’t indicted because special prosecutor Leon Jaworski believed doing so was the responsibility of the House. But there’s no legal principle involved. Mueller could easily come to a different conclusion and recommend indicting the president if the House won’t act.

Under the statute governing special counsels, Mueller is supposed to deliver a report on his findings to the Attorney General. But Sessions has recused himself, and his deputy, Rod Rosenstein, is involved in the obstruction case and will thus almost certainly have to recuse himself, too. So who will even receive Mueller’s report? And what if Justice Neil Gorsuch--appointed by Trump--is the deciding vote on the constitutionality of Trump's firings, pardons or indictment? Yikes.

Yes, liberal talk of dumping Trump is premature. The Republican-controlled House almost certainly won’t impeach him on obstruction of justice. Democrats would probably do so in 2019 if they win back control, but removing him from office takes a two-thirds majority in the Senate. Trump—with Dershowitz’s help?— would likely win his trial there, as Bill Clinton did, generating feverish support from his partisans as he fought the “witch hunt.”

We’re in deep and brackish waters now. “When the president does it, that means that it is not illegal,” Nixon told David Frost after he resigned. Trump no doubt believes the same and will act accordingly, the Constitution be damned.