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.

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-ABC News' Tal Axelrod

Republican National Committee Chairwoman Ronna McDaniel called the indictment "a blatant abuse of power from a DA focused on political vengeance."

"When our justice system is weaponized as a political tool, it endangers all of us," she tweeted.

Criminal prosecution proceedings typically start with an arrest and a court appearance, but legal experts say that on many occasions, especially in white-collar crimes, suspects aren't hit with charges or a visit from an officer until long after an official investigation is underway.

Typically, if a crime is being investigated, law enforcement agents will make an arrest, file initial charges and bring a suspect to be arraigned in court, Vincent Southerland, an assistant professor of clinical law and the director of the criminal defense and reentry clinic at NYU School of Law, told ABC News.

However, Southerland noted that prosecutors can start with the criminal indictment process in the beginning, especially if their case needs more evidence to press those charges.

Cheryl Bader, an associate clinical professor of law at Fordham University, told ABC News that such a move is common in white-collar criminal investigations that involve looking at delicate nuances in the state law and require more time.

Bader said investigations into prominent figures, such as the current investigation by the Manhattan district attorney's office into former President Donald Trump, also prompt prosecutors' offices to make their case to the grand jury in the most meticulous and thorough way possible.

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-ABC News' Ivan Pereira

The Democratic National Committee said in a statement Thursday, “No matter what happens in Trump’s upcoming legal proceedings, it’s obvious the Republican Party remains firmly in the hold of Donald Trump and MAGA Republicans."

The DNC vowed, "We will continue to hold Trump and all Republican candidates accountable for the extreme MAGA agenda that includes banning abortion, cutting Social Security and Medicare, and undermining free and fair elections.”

Sources familiar with the matter told ABC News the Manhattan district attorney’s office is also investigating a $150,000 payment to Playboy model Karen McDougal, who, like Stormy Daniels, claimed to have had an affair with Donald Trump.

The former president has denied having an affair with either woman and has called the investigation a witch hunt.

McDougal was paid for the rights to her story in August 2016 by American Media, publisher of the National Enquirer, which did not publish it, a practice known as catch and kill.

Michael Cohen, Trump’s former lawyer and fixer, has said he recorded Trump discussing reimbursement to American Media for the payment to McDougal, but the payment was never made.

Trump has not responded to ABC News' request for comment but in a 2018 interview with Fox News, he claimed he wasn't aware of any payment made to AMI to facilitate the alleged hush agreement.