NEW YORK, March 21, 2023 (BSS/AFP) - New York police tightened security Monday ahead of a possible historic indictment of Donald Trump over hush money paid to a porn actress, with the ex-president calling for mass demonstrations if he is charged.

Only a couple of dozen Trump supporters attended a protest in America's financial capital on Monday evening though, as a grand jury weighs an investigation by Manhattan District Attorney Alvin Bragg over the 2016 payment to Stormy Daniels.

Trump would become the first former or sitting president to be charged with a crime if an indictment is filed -- a move that would send shockwaves through the 2024 White House race, in which the 76-year-old is running to regain office.

Bragg, an elected Democrat, has not confirmed any plans publicly, but has put key witnesses in front of the jury in recent weeks and offered Trump the opportunity to testify.

Trump said over the weekend that he expects to be "arrested" on Tuesday and urged supporters to "Protest, take our nation back!" although his lawyer said the comments were based on media reports and not any fresh action by prosecutors.

Some US media said the panel could vote to indict when it returns on Wednesday after it interviewed its final witness, lawyer Robert Costello, on Monday.

The NYPD geared up for an unprecedented arrest, which would see an ex-leader of the United States fingerprinted and possibly even handcuffed, by erecting barricades outside Bragg's office and Trump Tower on Fifth Avenue.

More than a dozen senior police officials met with mayoral aides on Sunday to discuss security and contingency plans for protests, the New York Times reported.

NBC News said police and other law enforcement agencies had conducted "preliminary security assessments," including placing a security perimeter around the Manhattan Criminal Court where Trump would likely appear before a judge.

Senior Democrats have warned that Trump's calls could trigger a repeat of the violence that his supporters unleashed on the US Capitol in January 2021.

In an online group named "The Donald," some Trump supporters called for a "national strike" and "Civil War 2.0" to protect Trump and protest any arrest.

But there was no indication of a large movement and figureheads for Trump such as his sons and leading commentators have not openly urged action in the streets as they did after the 2020 election, when President Joe Biden defeated Trump.

A small protest organized by the New York Young Republican Club in lower Manhattan passed peacefully.

- Trump's many legal woes -

Bragg's inquiry centers on $130,000 paid weeks before the 2016 polls to stop Daniels from going public about an affair she says she had with Trump years earlier.

Trump's ex-lawyer-turned-enemy Michael Cohen says he made the payment and was later reimbursed.

The payment to Daniels, if not properly accounted for, could result in a misdemeanor charge for falsifying business records.

That might be raised to a felony if the false accounting was intended to cover up a second crime, such as a campaign finance violation.

Cohen testified in front of the grand jury last week, while Daniels is cooperating with prosecutors.

An indictment would begin a lengthy process that could last several months, as the case would face a mountain of legal issues and move toward jury selection.

Trump has denied having had an affair with Daniels and has blasted the investigation as a "witch hunt." His vice president Mike Pence described the probe as a "politically charged prosecution."

Trump is facing several criminal investigations at the state and federal level over possible wrongdoing that threaten his new run at the White House.

In Georgia, a prosecutor is investigating Trump and his allies' efforts to overturn his 2020 election loss in the southern state. The grand jury in that case has recommended multiple indictments, the forewoman revealed last month.

The former president is also the subject of a federal probe into his handling of classified documents as well as his possible involvement in the January 6 rioting.

Some observers believe an indictment bodes ill for Trump's 2024 chances, while others say it could boost his support.