The indictment of Donald Trump marks an unprecedented development in the country's history -- the first time a former president has ever faced criminal charges.
Historians say that not since Richard Nixon had there been the real prospect of a commander-in-chief being formally accused of a crime, though Nixon avoided that fate after being pardoned by successor Gerald Ford.
Trump's indictment by a New York City grand jury was confirmed to ABC News by multiple sources on Thursday. While the charge or charges against him remain unclear, he had been under investigation by Manhattan District Attorney Alvin Bragg over money paid to adult film actress Stormy Daniels during Trump's 2016 presidential bid to stop Daniels from going public about what she claimed was an affair with Trump.
Trump denies any wrongdoing, saying he is being politically persecuted, and maintains he never had a relationship with Daniels.
He has defended the $130,000 he paid Daniels, with his attorneys describing it as extortion.
The indictment -- resulting from just one of multiple investigations into Trump -- comes in the early stages of the 2024 presidential race as Trump seeks the Republican nomination for a third time.
Beyond the uncertainty that being indicted inserts into Trump's comeback campaign, the legal development thrusts him, the judicial system and perhaps the country itself into uncharted waters.
"There's nothing even remotely like it in American history. The closest that we come is Richard Nixon back in 1974, after he had left the White House upon resignation in the face of almost certain impeachment by the House of Representatives," said ABC News presidential historian Mark Updegrove.
The only other point of comparison is when then-Vice President Aaron Burr killed Alexander Hamilton in a duel in 1804 and, after leaving office, was arrested, tried and found innocent around charges of staging an insurrection, Updegrove said. (Decades alter, in a separate matter, then-President Ulysses S. Grant was arrested in 1872 related to speeding on his carriage.)
"With Trump, it's a very different circumstance," Updegrove said.
Unlike Nixon, who was ultimately pushed out of office under bipartisan pressure, Trump has gotten backing from his fellow conservatives.
And unlike Nixon, Trump has no hope of a presidential pardon from his successor, Democrat Joe Biden.
President Ford pardoned Nixon in September 1974 -- igniting instant controversy -- and said in a speech to the public that his decision was in the interest of ending the prolonged fallout from Watergate and its cover-up, which had roiled the country and led to a slew of political resignations or officials being charged.
In his pardon speech, Ford called Nixon a "longtime friend" who had "suffered enough, and will continue to suffer" amid "serious allegations and accusations [that] hang like a sword."
Attorney Nick Akerman, who helped investigate Nixon while working for Watergate special prosecutor Leon Jaworski, told ABC News he believed Nixon "could have been indicted" but Jaworski decided the appropriate channel for bringing charges against a sitting president was through Congress.
"He was even named as an unindicted co-conspirator in the cover-up trial," Akerman said.
By the time Nixon resigned from office, and the idea of an indictment could be revisited, the pardon from Ford came just weeks later, Akerman said.
Updegrove said the political mood around Nixon is much different than now, around Trump.
"It was Republicans, as well as Democrats, who saw the misdeeds of Watergate as being an indication that Richard Nixon was not fit for office," he said. "You have so much more division in Washington and in the country today than you did back then. So, I'm not sure that these charges will really matter what the Republican base. We'll see."
Even before the indictment came down against Trump, leading members of the GOP cast him as the victim of a partisan vendetta by Bragg, a Democrat, with House Speaker Kevin McCarthy telling GOP-led House committees to investigate if federal funds were used as part of Bragg's investigation.
"I think most people in Trump's base are of the mind that New York is a liberal bastion, and it's those people first who would be out to get Donald Trump. I think they subscribe to the notion that there is a 'deep state' [of anti-Trump forces in the government], there is a conscious effort to get Donald Trump, and it plays into this brilliant us-versus-them, they're-all-out-to-get-me narrative that Trump has been so successful in propagating," Updegrove said.
The indictment may ultimately play a minor role in Trump's legacy by virtue of the fact that opinions are already settled on Trump's scandal-plagued personal life and the other investigations into his conduct involve government activity, Updegrove said.
Those probes include his handling of classified documents while out of office as well as his push to overturn the results of the 2020 presidential election.
"Those are more serious as they relate to matters of the state," Updegrove said. "But this is a personal thing, which I think makes it a fundamentally different thing. We know that Donald Trump has character blemishes on his personal side. I think people were willing, particularly in his base, were willing to overlook them because he was willing to uphold the policies that they advocated. That's a different matter altogether."
"I think it's probably a big part of a chapter on a book about Donald Trump. I don't see this as the major thing," Updegrove said.
Still, that doesn't take away from the historic nature of the indictment, he said, adding to a notorious resume for Trump that already includes being the first president to be impeached twice -- once over allegations he withheld aid to Ukraine to force the launch of a probe into Biden and once over Trump's role in the Jan. 6, 2021, insurrection. He was acquitted by the Senate in both cases.
Updegrove said Trump's indictment and the related proceedings -- being processed by the criminal justice system, being summoned to court -- have immense symbolic power because he was president.
Ford acknowledged as much when granting clemency to Nixon, and he said then that he worried about the alternative. In his official proclamation of a pardon, Ford contended that "it is believed that a trial of Richard Nixon, if it became necessary, could not fairly begin until a year or more has elapsed. In the meantime, the tranquility to which this nation has been restored by the events of recent weeks could be irreparably lost by the prospects of bringing to trial a former President of the United States."
Trump now becoming the first president on the brink of a criminal trial permanently changes how he is remembered, Updegrove said.
"In the photo gallery that will be in that book, you are going to see as one of the larger photographs the mugshot of Trump, based on these proceedings. That's a pretty big deal. That in itself is a pretty big deal," Updegrove said. "It becomes a symbol, more or less, of the Trump presidency, not just a reflection of this particular aspect of Trump's legacy. It's the bigger picture of Donald Trump."
More broadly, Updegrove said, Trump's indictment reflects back on the state of the country.
"There was a time when honesty and integrity were the bedrock of the presidency," he said, citing George Washington and the myth of the cherry tree, or Abraham Lincoln's "Honest Abe" nickname, contrasted with Trump's habit of falsehoods.
"Now Trump has been indicted with other possible indictments to come," Updegrove said. "One has to wonder, does the morality of our president still matter to the American people or does it just matter that your side wins?"
ABC News' Alexandra Hutzler contributed to this report.