(CNN) Donald Trump has been president for barely three-and-a-half months, but he's already fired two of the country's highest-ranking federal law enforcement officials and twice set off alarm bells for Democrats who have crowed about a pending constitutional crisis.

They sounded for the first time in January when he sacked acting Attorney General Sally Yates after she instructed Justice Department lawyers not to defend his first travel ban order in court. Trump replaced Yates with with Dana Boente, the US attorney for the Eastern District of Virginia, who was sworn in the same night.

Boente moved down the ladder when the Senate confirmed Trump nominee Jeff Sessions and was then chosen to become the interim head of the DOJ national security division after Rod Rosenstein got the thumbs up as deputy attorney general.

Now, Sessions and Rosenstein are at the center of another self-made political pickle. Trump cited their recommendations when he dismissed FBI Director James Comey on Tuesday night. Comey, of course, was leading a wide-ranging federal investigation into potential connections between Trump's 2016 campaign and Russia.

With that, many asked (again) if this was a constitutional crisis. And I (again) posed the question to Jennifer Chacón, a professor at the University of California Irvine School of Law, and an expert on separating rhetorical flights from legal realities.

The first time we spoke , after Yates was fired, Chacón said, "No -- not yet," and offered this helpful definition: "A crisis would be a situation where there was a genuine concern that one branch of the government was not acting constitutionally, and no checks seem to be operating on that branch."

With that in mind, it wasn't too much of a surprise when Chacón emailed Thursday to confirm that, nope, "still no constitutional crisis!"

Simply stated, an FBI director (like an acting attorney general) serves at the pleasure of the president. Comey's work, as has been reported in excruciating detail, was no longer a source of pleasure to Trump. And so it goes.

There are certainly "bad optics" and "serious ethical questions," Chacón said, especially with regard to Sessions' involvement, "but in my view this does not necessarily raise constitutional questions."

The fact is that "constitutional crisis" has no textbook definition.

Legal scholars Sanford Levinson and Jack Balkin published an extensive article in 2009 on the term and what it did and did not mean. Mostly they proposed that Americans (yes, the media in particular) had lowered the bar too far, and because "conflict between political actors is the norm and not the exception in American constitutional life, the idea of constitutional crisis must be far narrower."

They sought to make a special distinction between a constitutional crisis and "mere political crises." Richard Nixon's infamous decision to fire Archibald Cox, the special prosecutor in the Watergate case? That's a political crisis in their estimation. What could have vaulted that mess into the constitutional realm, they argued, came a little later, when Nixon was faced with a Supreme Court order -- effectively pitting the judiciary branch against the executive -- to turn over the Watergate tapes.

Nixon ultimately complied with the court and, not long after, resigned in disgrace.

JUST WATCHED Watch Nixon resign the presidency Replay More Videos ... MUST WATCH Watch Nixon resign the presidency 03:31

Which brings to mind one last variable: Congress. The Supreme Court issued its unanimous order on July 24, 1974, as the House Judiciary Committee was preparing to open debate on articles of impeachment . By August 9, Nixon had left office.

But what if the House had not been prepared to send Nixon packing anyway? If there had not been significant pressure from Capitol Hill, from Democrats and Republicans, would Nixon have felt less pressure to obey the court order?

The current situation is very different. Trump fired the very man who happened to be investigating ties between his campaign associates and Russia at a time when American intelligence agencies have said the Russian government was trying to hurt Hillary Clinton.

What happens next, particularly on Capitol Hill, where members of the President's party are running separate investigations with help from Democrats, will be key to determining if a political crisis begins to threaten the checks and balances that are supposed to keep the US government working.