New York City and Washington, D.C., law enforcement were setting up barricades on Tuesday and have alerted reserve forces of possible mobilization ahead of the potential indictment of former President Donald Trump by a Manhattan criminal court, expected to come this week.

The indictment of a former president would be an unprecedented moment in American history, and how Trump’s supporters will react is unknown.

The commanding officer of the New York City Police Department’s operational division sent a memo asking all uniformed police divisions to be prepared for mobilization at any time in case of protests and civil unrest, according to local press reports.

The U.S. Capitol Police in Washington, D.C., have set up barricades around the Capitol building. A senior congressional source told CBS News that Capitol Police have also mobilized more officers to be on-site for the week, but are not aware of any planned protests at the moment.

Analysis: Can Trump still run for president in 2024 if he’s found guilty of a crime?

Saturday, Trump took to social media to call for protests if he is indicted. “PROTEST,” he urged his supporters, “TAKE OUR NATION BACK!”

Multiple outlets reported barricades being set up outside the Manhattan Criminal Court in New York City where a grand jury is reportedly close to making a decision on whether to press charges against Trump.

The grand jury was summoned by Manhattan District Attorney Alvin Bragg to determine if charges should be filed. The possible charges involve Trump’s payments to Stormy Daniels in 2016 through his then-attorney that were allegedly recorded as a legal fee rather than a business record, which is a misdemeanor. Trump could also be charged with a federal campaign finance disclosure failure and cover-up, which is a felony.

A grand jury is used in some states to determine if there is “probable cause” to believe an individual has committed a crime and should be put on trial.

When will the Manhattan grand jury decide whether to charge Trump?

The Manhattan grand jury proceedings are not open to the public or the media. Trump suggested Saturday he could be indicted as soon as Tuesday, but some outlets are reporting the grand jury is scheduled to hear from more witnesses Wednesday, with a possible vote later that day or later this week.

Only 12 of the 23-member grand jury need to vote in favor of prosecution in order for Trump to be charged.

Trump was offered an opportunity to appear before the grand jury, but he refused, according to his lawyers. Politico reported that prosecutors rarely allow a grand jury to proceed to a vote unless they are confident the jury members will vote for prosecution.

If a vote for prosecution takes place, the court will notify Trump’s lawyers, at which point it’s plausible the public could learn about the indictment from Trump.

What happens next if Trump is charged?

If Bragg files charges, Trump must surrender himself to New York law enforcement and proceed with booking and arraignment.

Booking and arraignment consists of posing for a mug shot, taking finger prints and appearing in court before a judge. It is unclear how Secret Service will take part throughout the process, since they are charged by federal law with protecting former presidents.

The prospect of Trump handcuffed and perp walked in front of the media is all possible, but this could depend on terms of surrender negotiated by his attorneys.

A virtual arraignment for non-violent, white collar crimes has been used in the past, but sources told Fox News that Bragg is opposed to it in this case. This would require Trump to surrender in person to New York authorities.

With Trump standing before a judge, the grand jury’s indictment would be unsealed by district prosecutors and read publicly to the former president. He would then be asked if he pleads guilty or not guilty.

The judge would then set a trial date and Trump would most likely be able to return to his home in Florida.

There is no time limit between a grand jury indictment and when Trump must be arraigned in front of a judge. However, if the grand jury votes to indict him this week, it is widely expected Trump will surrender to New York authorities sometime next week.