Manhattan District Attorney Alvin Bragg's office said in a statement that it has contacted former President Donald Trump's attorney "to coordinate his surrender" for arraignment on a state Supreme Court indictment, noting that it remains under seal.

"Guidance will be provided when the arraignment date is selected," the office said.

In the wake of the indictment, all officers with the New York Police Department have been ordered to show up in uniform Friday morning for deployments around New York City, police sources told ABC News.

There are no credible threats, according to the mayor's office.

The indictment of Donald Trump marks an unprecedented development in the country's history -- the first time a former president has ever faced criminal charges.

Historians say that not since Richard Nixon had there been the real prospect of a commander-in-chief being formally accused of a crime, though Nixon avoided that fate after being pardoned by successor Gerald Ford.

Read more here.

-ABC News' Tal Axelrod

Republican National Committee Chairwoman Ronna McDaniel called the indictment "a blatant abuse of power from a DA focused on political vengeance."

"When our justice system is weaponized as a political tool, it endangers all of us," she tweeted.

A spokesman for New York City Mayor Eric Adams issued a statement Friday evening condemning the threatening letter sent to District Attorney Alvin Bragg that included powder later deemed non-hazardous.

"While we cannot comment on the specifics of any ongoing investigation, no public official should ever be subject to threats for doing his or her job," the statement read.

The spokesman added, "I'm confident that every elected official in the City, including Manhattan DA Bragg, will continue to do their work undeterred, and anyone found to be engaging in illegal conduct will be brought to justice."