An indictment of Trump, who is seeking the White House again in 2024, would be an unprecedented moment in American history, the first criminal case against a former U.S. president.

Law enforcement officials are bracing for protests and the possibility of violence after Trump called on his supporters to protest ahead of a possible indictment.

An indictment could also test a Republican Party already divided over whether to support Trump next year, in part due to his efforts to undermine his 2020 election loss.

Trump denies any wrongdoing and has slammed the Manhattan district attorney’s office probe as politically motivated.

The grand jury has been probing Trump’s involvement in a $130,000 payment made in 2016 to the porn actor Stormy Daniels to keep her from going public about a sexual encounter she said she had with him years earlier. Trump lawyer Michael Cohen paid Daniels, whose real name is Stephanie Clifford, through a shell company before being reimbursed by Trump, whose company, the Trump Organization, logged the reimbursements as legal expenses.

Earlier in 2016, Cohen also arranged for former Playboy model Karen McDougal to be paid $150,000 by the publisher of the supermarket tabloid The National Enquirer, which then squelched her story in a journalistically dubious practice known as “catch-and-kill.”

Trump’s company “grossed up” Cohen’s reimbursement for the Daniels payment to defray tax payments, according to federal prosecutors who filed criminal charges against the lawyer in connection with the payments in 2018. In all, Cohen got $360,000 plus a $60,000 bonus, for a total of $420,000.

Manhattan District Attorney Alvin Bragg’s team appears to be looking at whether Trump or anyone committed crimes in New York state in arranging the payments, or in the way they accounted for them internally at the Trump Organization.

In a word, yes. Longstanding Justice Department policy prohibits the federal indictment of a sitting president, but Trump, two years out of office, no longer enjoys that legal shield. And the New York case is not a federal probe anyway.

A grand jury is made up of people drawn from the community, similar to a trial jury. But unlike juries that hear trials, grand juries don’t decide whether someone is guilty or innocent. They only decide whether there is sufficient evidence for someone to be charged. Grand juries exist in the federal court system and in many states.

Proceedings are closed to the public, including the media. There is no judge present nor anyone representing the accused.

Prosecutors call and question witnesses, and grand jurors can also ask questions. In New York, the person who could be indicted may ask for a certain witness, though it’s up to grand jurors.

New York grand juries have 23 people. At least 16 must be present to hear evidence or deliberate. Twelve have to agree there is enough evidence in order to issue an indictment. The grand jury may also find there is not enough evidence of a crime or direct the prosecutor to file lesser charges.