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.

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-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.

Manhattan District Attorney Alvin Bragg on Friday again resisted the House GOP investigation of his office’s prosecution of Trump.

Bragg’s legal counsel called the inquiry “illegitimate incursion” into a legitimate investigation.

The House Republicans -- Reps. Jim Jordan, James Comer and Bryan Steil -- have said they want to find evidence of federal funds used to investigate Trump. But Bragg’s office said they were merely doing Trump’s bidding.

“Finally, as you are no doubt aware, former President Trump has directed harsh invective against District Attorney Bragg and threatened on social media that his arrest or indictment in New York may unleash 'death & destruction.' As Committee Chairmen, you could use the stature of your office to denounce these attacks and urge respect for the fairness of our justice system and for the work of the impartial grand jury," counsel Leslie Dubeck wrote in a letter to the lawmakers.

"Instead, you and many of your colleagues have chosen to collaborate with Mr. Trump’s efforts to vilify and denigrate the integrity of elected state prosecutors and trial judges and made unfounded allegations that the Office’s investigation, conducted via an independent grand jury of average citizens serving New York State, is politically motivated.”