Trump advisers said they were still discussing among themselves, and with Trump, the logistics of an indictment – including whether the former president would have to travel to New York to appear in court, whether he could avoid having his mug shot released or any other public spectacle, and whether, if indicted, he will hold a news conference to discuss it.

The office of Manhattan District Attorney Alvin Bragg (Democrats) did not respond to a request for comment on Saturday.

Secret Service officials were caught by surprise on Saturday morning by Trump’s post predicting a Tuesday arrest, according to a person with knowledge of the discussions who spoke on the condition of anonymity to discuss sensitive planning. During discussions on Friday in preparation for Trump’s possible indictment in New York, Secret Service leaders expected that Trump’s legal team would immediately notify them if his lawyers heard about any planned indictment.

The Secret Service officials also expect that the district attorney’s office would negotiate terms under which Trump could voluntarily turn himself in. The lawyers have provided no such notification, according to the person familiar with the Secret Service planning.

Trump’s post was reminiscent of his call in late 2020 for supporters to come to Washington on January 6 to protest the election results: “Be there, will be wild!” On Saturday, Truth Social users posted comments such as “all hell will break loose” in response to the possibility of Trump’s indictment.

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Mary McCord, director of a democracy advocacy centre at Georgetown Law School, said Trump is whipping up extremists who could engage in violence.

“Trump knows the call-and-response impact of his words on his most ardent followers,” McCord said. “His call to ‘take our nation back’, like his last-ditch call for them to ‘fight like hell’ on January 6, is not only the request but the permission for them to act, violently if necessary.”

“Protest is protected and valued in America,” she said, “but violence and incitement to violence is unlawful and unprotected by the First Amendment.”

McCord and her organisation repeatedly warned the FBI and local authorities in the weeks leading up to January 6, 2021, that domestic extremists egged on by Trump’s call to his Washington rally were planning to target the Capitol that day and attack police and lawmakers.

A preliminary security planning meeting was held recently involving the district attorney’s office and the New York Police Department, according to one person with knowledge of the planning. That person spoke on the condition of anonymity to discuss a sensitive matter.

Law enforcement and court officials – including the NYPD, the Secret Service, New York State Court officers, the Manhattan district attorney’s office and judges – are expected to meet early next week to discuss security and logistics for Trump’s potential first court appearance, according to people with knowledge of the planning. The officials are likely to discuss issues including how to handle a potential rush of protesters around the perimeter of 100 Centre Street, the borough’s main criminal courthouse.

“It’s an unbelievable security nightmare, and it’s going to inconvenience everybody at the courthouse whatever day we do it,” said Dennis Quirk, head of the New York State Court Officers Association.

A Trump indictment would be a stunning moment – a former president, who faces a slew of investigations of his handling of classified documents and the January 6 attack, charged over a payment to adult-film star Stormy Daniels.

The case involves a $US130,000 payment that Michael Cohen, a former Trump attorney, made to Daniels before the 2016 presidential election and whether it was made to keep her quiet about allegations that she and Trump had an affair. Trump has denied having an affair with Daniels and described the payments as extortion.

Cohen has acknowledged making the payment, saying he did so expecting to be reimbursed; that refund was allegedly documented as payment for legal work.

The case had been examined for years by authorities, but prosecutors have until now declined to pursue charges against Trump. But in recent weeks, Bragg has escalated the case.

Meanwhile, Trump’s team has begun fundraising on the prospect of his arrest, after the FBI raid of his Mar-a-Lago home last year led to his best fundraising days since leaving the White House, The Washington Post reported.

“MANHATTAN D.A. COULD BE CLOSE TO CHARGING TRUMP,” one pitch on Saturday morning read. “Patriot – With the Deep State gunning for President Trump with phony witch hunts like never before, we had to be sure you saw the *private and secure* message he wrote for YOU. See below!”

Trump and his team are preparing to go to “political war”, in the words of one adviser, to impugn the credibility of Bragg, Cohen and Daniels. Trump, who was kicked off numerous social media platforms after the January 6 attack, has been getting his accounts back. On Friday, he posted on Facebook and YouTube, telling his followers he was back online.

Trump also wants to force Republicans to defend him against the investigation publicly, the adviser said. Many of his advisers and surrogates began attacking Bragg on Saturday morning, and a Trump-aligned PAC, MAGA Inc., sent a news release tracking which of Trump’s fellow 2024 GOP presidential hopefuls had come to his defence and which had not.

House Speaker Kevin McCarthy (a Republican from California) on Saturday called for a congressional inquiry into the Manhattan district attorney. “I’m directing relevant committees to immediately investigate if federal funds are being used to subvert our democracy by interfering in elections with politically motivated prosecutions,” McCarthy wrote on Twitter.

“Stop the Steal” rally organiser Ali Alexander, in a tweet in response to Trump’s post, seemed to be backing away from Trump’s calls for action. Alexander wrote that people who protest in New York City “will be jailed or worse”. He instead urged his followers to help the families of people who were arrested on charges related to the January 6 attack.

“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-Largo,” Alexander posted on the Telegram platform. “Now, I’m retired. I’ll pray for him though!”

Trump supporter and anti-abortion activist Frank Pavone, however, appeared eager to call upon his supporters. “Oh yes, we will protest, and it will be overwhelmingly resounding!” Pavone wrote.

Trump wrote a second post on Truth Social later in the day calling on his supporters to “PROTEST, PROTEST, PROTEST” in what appeared to be complaints about the Biden presidency.

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A special counsel appointed by Attorney General Merrick Garland is leading parallel investigations of Trump’s role in efforts to block the 2020 election results and the potential mishandling of classified documents at Mar-a-Lago. Separately, Georgia prosecutors are nearing the end of their probe of his efforts to overturn that state’s 2020 election results.

Advisers have said Trump has been focused on the investigations intently in recent months and has long dreaded a potential arrest or indictment.

After posting on Truth Social, Trump played golf at his club in Jupiter, Florida. He was scheduled to fly later on Saturday to a national wrestling tournament in Oklahoma.