Thousands of soldiers and law enforcement officers descended on the nation's capital. Steel fences encircled the White House. Heavily armed officers met protesters with flash-bang grenades and chemical agents.
In response to the president's threats to deploy military assets in a domestic setting, former military brass and departed Trump aides leveled a succession of pointed warnings. And lawmakers have sought reassurances that any future spike in violence or disease won't bring a military crackdown.
Even though Trump has been prone to using fiery language for spectacle, and appears to have retreated from flexing about using more force, his critics maintain there are fresh reasons to worry. He could seek to further expand the boundaries of his power, they told ABC News, with several adding ominously that there are two words they fear most: martial law.
"This president has indicated no respect for limitations on his authority," U.S. Sen. Angus King, a Maine independent, told ABC News on Friday. "What is he capable of? I think the answer is, pretty much anything."
Presidents have imposed martial law -- giving military commanders the authority to make rules or take actions deemed necessary to restore order -- only rarely and in targeted ways over the course of the nation's history. The most striking example, during desegregation in the Deep South, was brief and limited. But taken to the extreme, the power could lead to the suppression of basic liberties, experts said.
King is one of several senators, most of them Democrats, who have written to the Trump administration in recent weeks seeking clarity on the president's intentions. He said he and others have not appreciated seeing Trump musing publicly about extending the limits of his authority.
Trump and his administration have long floated an expansive approach to executive power, with the president arguing in a June 2019 interview with ABC News that Article II of the Constitution "allows me to do whatever I want," and arguing this year that he has "absolute immunity" from subpoenas.
In 2017, Trump threatened to "send in the feds" to Chicago to quell violence there, and raised objections from critics that his deployment of troops to the Southern border to help with immigration control violated the Posse Comitatus Act, which limits the law enforcement capacity of active duty military troops.
Trump's flexing has grown more frequent since early spring, when the nation was beset by a pandemic and then by mass demonstrations around the country. During an April 14 White House briefing, on one of the darkest days of the coronavirus outbreak, Trump made his views on the subject clear by discussing his desire to overrule governors on reopening their states.
"When somebody is the president of the United States, the authority is total, and that's the way it's got to be," Trump said. "It's total. Total."
Though he dialed that rhetoric back the following day, concerns from the president's critics have only grown with the waves of protests and unrest that have followed the release of harrowing video showing George Floyd dying with a Minneapolis police officer's knee on his neck for nearly nine minutes.
In addition to thousands marching and gathering peacefully across the country, there were also incidents of destruction and violence, with looters destroying storefronts, vandals setting fire to police cars and other buildings, and some attacking police officers and leading a police precinct in Minneapolis to be abandoned. Some states authorized the national guard to assist law enforcement, but others, like New York, did not. On May 28, Minnesota Gov. Tim Walz began activating the states' national guard to provide support to local law enforcement in Minneapolis.
During one White House speech last week, Trump declared his intent to enlist the military to quell outbreaks of violence by invoking the rarely-used Insurrection Act of 1807.
At that very moment, his aides had deployed military police from the D.C. National Guard and federal law to forcefully clear protesters from Lafayette Square, across from the White House, well before curfew, to enable him to pose for a photo with a bible in his hand at a neighboring historic church, damaged by fire amid the protests.
That move brought an unexpectedly sharp rebuke from a cast of retired military leaders, including the former chairman of the Joint Chiefs of Staff, retired Adm. Mike Mullen -- who served during the George W. Bush and Obama administrations -- Trump's former defense secretary, retired Gen. James Mattis, and retired Gen. Martin Dempsey.
Dempsey told ABC's Martha Raddatz on "This Week" Sunday that he worried Trump's threat to deploy the military on U.S. streets "would put the active duty military in a position where its relationship with the American people would be adversely affected."
Mattis was even more pointed, writing: "We must reject and hold accountable those in office who would make a mockery of our Constitution."
One reason for the alarm, several legal and constitutional scholars told ABC News, is that military control can be very hard to contain once the powers of civil control have been relinquished.
"There is no off switch," said Stephen Dycus, a professor at Vermont Law School, and the lead author of a casebook on the subject of executive power.
No precedents for martial law
Dycus said no modern president has moved to expand military power so broadly as to slide the nation toward martial law in peacetime -- where military authority overrules the nation's system of laws. But he worries about the potential response Trump may consider should the coronavirus resurge, or should civil unrest expand.
On Wednesday, Alan Dershowitz, one of President Trump's longtime personal advisers, took the unusual step of writing an opinion column in The Hill about the prospects of martial law, saying the nation has not reached the point where military force is justified.
"What then would the courts do if the president were to declare martial law and have the military detain protesters?" he wrote. "The answer here is clear. No one knows. There are no direct precedents for such an action when our nation is in peacetime."
Dershowitz wrote that martial law can be invoked by the president -- or by a military commander -- only when he or she thinks it is necessary to prevent a total breakdown in society.
"We are definitely not experiencing an invasion, nor do the current disturbances, violent as some but not others have been, qualify as a rebellion," Dershowitz wrote.
The same day, White House Press Secretary Kayleigh McEnany was asked about the possibility martial law could be imposed in Washington, D.C., to protect historic monuments, and she replied, "I have not heard that discussed."
Inside the White House, discussions about power
Interpreting the words of President Trump can often be challenging. A showman with a knack for grabbing headlines, he has more than once breathed life into inflammatory notions -- like seeking a third term or threatening North Korea with "fire and fury like the world has never seen" -- only to dial back his rhetoric in the days following.
Still, he has also shown a frequent penchant for strongman tactics and imagery -- once promoting the idea of marching a military parade down Pennsylvania Avenue.
And inside the White House, lawyers have quietly and vigorously been exploring the boundaries of presidential power and the extent to which it may be expanded, sources told ABC News.
Those efforts intensified after the April briefing when Trump declared he had total authority to open states' economies and said he has seen "numerous provisions" that say as much. The president had not been shown anything by the White House lawyers that stated that, sources said at the time. Trump never acted on the threat.
Since then, even as unsettling episodes of looting and unrest spread, the president never went so far as to consider anything approaching martial law, sources familiar with internal White House deliberations said.
The White House legal team rushed to prepare options ahead of the president's Rose Garden address one week ago. Conversations within the president's inner circle centered on domestic military options available to the commander in chief, senior administration officials said. One plan involved invoking the Insurrection Act, which permits the president to deploy armed forces to deal with civil disorder, as President George H.W. Bush did briefly during the 1992 civil unrest in Los Angeles.
Attorney General Bill Barr cited his role advising President Bush to make this decision during the riots, during an interview with CBS's "Face the Nation." Barr said he also believe the president would have the power to do so even if a governor of a particular state didn't request or approve the deployment, which he characterized as a "last resort" option.
As the week of unrest wore on, and violent clashes, and incidents of vandalism and looting began to wane, sources said the president began to cool to the idea. Ultimately, nearly one week after National Guard troops were deployed near the White House and around Washington, D.C., the president said on Sunday he ordered them withdrawn.
"I have just given an order for our National Guard to start the process of withdrawing from Washington, D.C., now that everything is under perfect control," Trump tweeted Sunday, as peaceful protests in the nation's capital continued over the weekend. "They will be going home, but can quickly return, if needed. Far fewer protesters showed up last night than anticipated!"
King speculated that strong backlash to heavy-handed military tactics during those opening hours may have given Trump pause. "I think response to what happened in Lafayette Square has been so overwhelming, the president is thinking twice," King said.
He and other Trump critics told ABC News they learned enough from the episode to ask more about the White House thinking in case conditions worsen in the fall.
Secretive emergency plans
While sources told ABC News that much of the legal work in the White House has centered on the response to coronavirus, and later the nationwide protests, one expert said there are longstanding blueprints for the president to assume more power during an emergency that date back to the Cold War and are revised periodically.
They are called the "presidential emergency action documents," and they were the subject of a New York Times op-ed in April co-authored by Elizabeth Goitein of the Brennan Center for Justice at New York University School of Law.
Goitein said they consist of draft proclamations, executive orders and proposals for legislation that can be quickly deployed to assert broad presidential authority in a range of worst-case scenarios.
"They are one of the government's best-kept secrets," she wrote. "No presidential emergency action document has ever been released or even leaked."
Goitein said people only know of their existence because, over the years, officials have made passing references to them in other public statements and documents. In 1987, the Miami Herald reported that Lieutenant Colonel Oliver North had worked on some elements of the secret emergency plans with the Federal Emergency Management Agency.
King, who sits on the Senate Intelligence and Armed Services committees, said it is "prudent and reasonable" for any president to prepare for an emergency and have contingency plans drafted.
"But I'd like to know what they are and the circumstances under which they would be exercised," he said about the reported documents. He has written to the administration to seek copies.
Goitein said she wrote about the secretive papers now for a reason.
She also noted the potential for a confluence of disruptive events that could strike this fall, especially if Trump has fallen behind in his reelection campaign.
"As polling comes out, if the economy suffers, if protests continue, if the virus resurges, he's going to feel backed into a corner," Goitein said.
"Emergency powers are dangerous, inherently," she said. "I think people understand that they need to be in the hands of people who are responsible and coolheaded."