A New York man was sentenced to 18 months in prison on Monday for threatening to kill the judge overseeing the criminal case against Trump administration national security adviser Michael Flynn, per the Washington Post.

Driving the news: Frank Caporusso pleaded guilty last April to leaving a threatening message in May 2020 on the voice mailbox of U.S. District Judge Emmet Sullivan over Flynn's case.

• "We are trained military people. We will be on rooftops. You will not be safe," the electronics salesman said in the voicemail to Sullivan's chambers, according to WashPost.
• "A hot piece of lead will cut through your skull. We'll start cutting down your staff. This is not a threat. This is a promise."

Why it matters: Threats to federal judges have increased 400% in the past five years. U.S. District Judge Trevor McFadden pointed to this spike in his sentencing remarks as he noted the threat would have caused "significant harm" to Sullivan and his staff, per Politico.

• Sullivan wrote in his victim statement that the threat "added to the cloud of concern hovering over judges nationwide as we preside over courtrooms where civility and respect for the rule of law seem to erode by the day," WashPost notes.

What else he's saying: While McFadden said he didn't believe Caporusso would carry out the threat, he described it as "despicable" and "calculated to instill a maximum amount of fear."

• McFadden noted that the threat was "intended to subvert the criminal justice system by intimidating" Sullivan "against continuing to preside over a high-profile case."
• "It was nothing less than an attack on our system of government," McFadden added, calling a Sullivan a "patriot," who "did not deserve this." "He certainly does not deserve to live in fear because of your actions," McFadded said.

Of note: Caporusso's plea to one count of one count of influencing, impeding, or retaliating against a federal official by threat came five months after then-President Trump pardoned Flynn — who pleaded guilty in 2017 as part of the Mueller investigation to lying to the FBI about his Russia contacts.