With his indictment by a Manhattan grand jury expected but its timing uncertain, former President Donald J. Trump declared on his social media site Saturday that he would be arrested on Tuesday, and demanded that his supporters protest on his behalf.
Mr. Trump made the declaration on Truth Social at 7:26. a.m., in a post written in all capital letters that ended by saying, “THE FAR & AWAY LEADING REPUBLICAN CANDIDATE AND FORMER PRESIDENT OF THE UNITED STATES OF AMERICA, WILL BE ARRESTED ON TUESDAY OF NEXT WEEK. PROTEST, TAKE OUR NATION BACK!”
The Manhattan district attorney’s office declined to comment. An adviser to Mr. Trump did not respond to a message seeking comment.
Although prosecutors working for the district attorney, Alvin L. Bragg, have signaled that an indictment of Mr. Trump could be imminent, there was no immediate indication as to why the former president appeared confident that he would be arrested Tuesday. People with knowledge of the matter have said that at least one more witness is expected to testify in front of the grand jury, which could slightly delay any indictment.
Three people close to Mr. Trump said that the former president’s team had no specific knowledge about when an indictment might come or when an arrest could be anticipated. One of those people, who were not authorized to speak publicly, said that Mr. Trump’s advisers’ best guess was that it could happen around Tuesday, and that someone may have relayed that to him, but that they also had made clear to one another that they didn’t know a specific time frame.
Mr. Trump, who faced his first criminal investigation in the late 1970s, has been deeply anxious about the prospect of being arrested, which is expected to include being fingerprinted, one of the people close to him said. When the Trump Organization’s former chief financial officer, Allen H. Weisselberg, was arrested in 2021, Mr. Trump watched in horror as television coverage showed Mr. Weisselberg flanked by officers in the courthouse and said he couldn’t believe what was being done to him.
The call for protests echoed Mr. Trump’s call to his supporters, in the waning days of his presidency, to join him for a rally in Washington on Jan. 6, 2021, the day President Biden’s win was to be certified by a congressional approval of the electoral college votes. At that rally, at the Ellipse near the White House, Mr. Trump then told supporters to march to the Capitol, where the certification was taking place.
Mr. Trump’s post urging his supporters to “PROTEST, TAKE OUR NATION BACK!” carried unmistakable echoes of the incendiary messages he posted online in the weeks before the attack on the Capitol. In the most notorious of those messages, he announced on Twitter that he would hold a rally in Washington on Jan. 6, 2021. “Be there,” he told his millions of followers, “will be wild.”
Investigators later determined that far-right extremist groups as well as ordinary Trump supporters read that tweet — posted on Dec. 19, 2020 — as a clear-cut invitation and almost immediately sprang into action, acquiring protective gear, setting up encrypted communications channels and, in one case, preparing heavily armed “quick reaction forces” to be staged outside of Washington for the event.
Leaders of groups like the Proud Boys and the Three Percenter militia movement also started to whip up their members with bellicose language as their private messaging channels were increasingly filled with plans to rush to Mr. Trump’s aid.
New York officials have been discussing security arrangements in and around the Manhattan Criminal Court in case of an indictment of Mr. Trump, according to people with knowledge of the planning, which was first reported by NBC News. He is expected to be charged in connection with hush-money payments his former fixer and lawyer, Michael D. Cohen, made to an adult-film actress who claimed to have had an affair with Mr. Trump.
Mr. Cohen made the $130,000 hush money payment to the porn star, Stormy Daniels, to bury her story of an affair with Mr. Trump.
The payment came in the run-up to the 2016 presidential election, and Mr. Trump subsequently reimbursed Mr. Cohen. Prosecutors are expected to accuse Mr. Trump of overseeing the false recording of the reimbursements in his company’s internal records. The records falsely stated that the payments to Mr. Cohen were for “legal expenses.”
There have been several signals that charges may be imminent: The prosecutors gave Mr. Trump an opportunity to testify, a right afforded to people who will soon face indictment, and have questioned nearly every major player in the hush money saga in front of the grand jury.
Mr. Trump has denied all wrongdoing, as well as having had an affair with Ms. Daniels.
Early Saturday morning, there was little evidence yet that Mr. Trump’s new demand for protests had been embraced by extremist groups.
But Ali Alexander, a prominent organizer of “Stop the Steal” rallies after the 2020 election, reposted a message on his Telegram channel on Saturday suggesting that he supported mass protest to protect Mr. Trump.
“Previously, I had said if Trump was arrested or under the threat of a perp walk, 100,000 patriots should shut down all routes to Mar-a-Lago,” Mr. Alexander wrote. “Now I’m retired. I’ll pray for him though!”
Lacking the platform provided by the White House or the machinery of a large political campaign, it is unclear how many people Mr. Trump is able to reach, let alone mobilize, using his Truth Social website.
And it remained unclear if he would repeat his call for action or increase the stakes with more aggressive language. But his political allies made plain this week that they were preparing for a political war on Mr. Bragg.
Some of Mr. Trump’s supporters responded of their own accord with violence after F.B.I. agents, acting on a search warrant, descended on Mar-a-Lago, his private club and residence in Florida, in August and carted away boxes of documents in an investigation into the former president’s handling of classified material.
Days after the search, an armed Ohio man who had posted online about his outrage over what happened at Mar-a-Lago tried to breach the F.B.I.’s field office outside Cincinnati. He was later killed in a standoff with local officers.
The unexpected Saturday morning salvo from the former president provided a preview of the kind of chaos that Mr. Bragg is likely to face if he moves forward with an indictment in the near future.
The district attorney, a former federal prosecutor and deputy New York attorney general, has some history prosecuting public officials. But he is unaccustomed to dealing with a figure as high-profile, erratic and pugilistic as the former president, and it is unclear how his office will deal with future outbursts from Mr. Trump.
William K. Rashbaum contributed reporting.