When White House lawyer Pat Cipollone sent a letter to Democrats this week, informing the House of Representatives that Donald Trump would not co-operate with their impeachment inquiry, it was a challenge that puts to the test the very foundation of American democracy, some constitutional scholars say.
But does this moment — in which a president stands accused of abusing his office and soliciting help from a foreign power for personal political gain — rise to the level of a constitutional crisis?
First, a history lesson on the document drafted in 1787, which created the frame of the U.S. government.
The U.S. Constitution created three co-equal branches of federal government: the executive, led by the president; the legislative, which includes Congress; and the judiciary, represented by the U.S. Supreme Court.
Built into the constitution is a system of checks and balances, so that one branch could not usurp another and the country would not fall victim to a tyrannical leader.
With the president (executive) now openly defying a House investigation (legislative), the question becomes: Is that system — and the very document upon which American democracy was built — now at risk?
The word "crisis" can be overused in today's heated political debate, and scholars say part of the challenge of assessing whether the current moment is one is there's no clear, agreed-upon definition of what qualifies as a constitutional crisis.
Yes, it is a constitutional crisis
For Dick Howard, a constitutional scholar at the University of Virginia, a constitutional crisis occurs when the president and Congress go beyond their usual stalemates over policy, to a standoff over a fundamental question of governance.
Secondly, he says, it's when both sides press their case to the limit, with no middle ground and no room for compromise.
The White House letter signed by Cipollone, which rejects the impeachment inquiry as "constitutionally invalid," is taking an absolute position, argues Howard. That means this moment is a crisis.
"[Trump] is basically throwing down a marker saying, 'No matter what you do, I'm not co-operating.' So it seems to me you have the standoff," he said. "You have the pressing of his claim to the limit."
Gloria Browne-Marshall, a constitutional law professor at John Jay College of Criminal Justice in New York, says the country has been in a constitutional crisis for a while — and this latest episode only adds to the case.
As she sees it, the crisis began when Trump signalled he wouldn't comply with subpoenas during Special Counsel Robert Mueller's investigation into Russian interference in the 2016 U.S. election.
By saying he'll stonewall Congress over impeachment, the president is "basically ignoring any of the boundaries on executive power and deciding, by himself, what he will and will not follow within the law," said Browne-Marshall.
The checks and balances between the branches of government only work if everyone plays by the rules, she says.
"The constitution is a document that's only as powerful as it is respected, and if [Trump] doesn't respect it, then that's what creates a constitutional crisis."
Georgetown law professor Heidi Li Feldman had been reluctant to call the situation a crisis, she said, but now feels she has no choice. The president's actions, bolstered by support and silence by members of his own Republican Party, show a blatant disregard for the checks and balances the constitution put in place, she argues.
"You cannot have — in a two-party system, in a constitutional democracy — one party simply OK'ing a president's claim to be entirely above the law and out of the reach of any accountability to the people," she said.
Her definition of a constitutional crisis uses a medical analogy: "It's a period of time when you're at an absolute turning point; either the disease will consume the patient or the disease will break and the patient will eventually recover."
The question left in Feldman's mind, she said, is whether constitutional democracy will survive the existential threat of a power grab by the executive branch.
No, it's not a constitutional crisis
For David Pozen, there's no denying that Trump is thumbing his nose at constitutional conventions with weak legal arguments. But the Columbia law professor argues that everything taking place is happening within the framework established by the U.S. Constitution.
What is happening now is the just opening shots in the impeachment process, he said — a process built into the constitution by the 55 men who created the document.
"I would say the White House is playing constitutional hardball within that process, but as long as we're within the terms of a constitutionally prescribed process, I think it's hard to say that we're in crisis mode."
From subpoenas, to court challenges, to moving forward on an impeachment vote without the president's co-operation, Pozen argues the House is far from incapacitated and has plenty of cards to play.
With the impeachment inquiry still in its early stages, Elizabeth Wydra is also reluctant to say America is in crisis.
"I think certainly the structures of our government and the protections in the constitution are being tested perhaps unlike ever before," said Wydra, who is president of the Constitutional Accountability Center, a Washington-based think-tank.
The White House letter breaks precedent, she says, because rather than push back on individual matters, it offers a blanket refusal to co-operate. According to Wydra, the arguments it contains are political and not constitutional.
"[White House lawyers] know perfectly well that their complaints and claims are really just partisan obstruction cloaked in constitutional terms. And I think it does a real disservice to the public by trying to distract and confuse the issue," she said.
One argument the White House letter makes is that impeachment would undo the 2016 election results.
But Wydra argues that the original framers of the constitution specifically created impeachment as the ultimate remedy for a leader accused of abusing power. "I think that this probably would be their worst nightmare, but I think it is a nightmare that they might have had," she said.
Georgetown constitutional law scholar Susan Low Bloch agrees.
"I would reserve the term 'constitutional crisis' for when things are not working and are scary," she said. "I see the constitution being tested right now — and so far it's holding up."
House Democrats could also respond with constitutional hardball of their own, Pozen argues, exploring rarely used options like arresting those who refuse to comply with subpoenas, or using their constitutionally assigned power of the purse to eliminate the budgets of obstructing offices, like the White House Counsel.
The Supreme Court and how this plays out
A resolution to this constitutional confrontation may come, in part, from the third branch of government, the judiciary.
While the U.S. Supreme Court can't decide itself if the president should be impeached or removed from office, it can arbitrate specific battles in the overall fight.
The last time the United States faced a test like this was when Richard Nixon refused a subpoena to hand over presidential tapes linked to the Watergate inquiry. His refusal became an article of impeachment for obstruction, and the Supreme Court eventually ruled he had to give up the recordings.
In that case, Nixon acquiesced, and eventually resigned.
What indisputably would constitute a crisis, the experts all agree, is if the Supreme Court ruled that Trump must comply with a subpoena — and he still refused.
Given Trump's history of criticism against judges and courts that rule against him, Browne-Marshall worries how he'd react to such a situation.
"We don't know what this president may do in response to clear instructions as to his limit of power," she said.
Practically speaking, it's not clear how this confrontation will be resolved, Feldman says; the answer to that lies in how far the president would push his argument for not co-operating with Congress.
Feldman further wonders what would happen if Trump is impeached by the House, then convicted in a Senate trial: Would he remove himself from office?
As for Howard, he believes the U.S. system will survive this test. And if it's not resolved in the courts or in Congress, then perhaps it will be at the ballot box next year.
"I'm guessing that one thing Trump is doing is simply playing for time, hoping he can run the clock and that you will have the election of 2020 before all this is resolved."