NEW YORK — A federal judge sentenced a New York man to 18 months in prison on Monday for threatening to kill two U.S. senators who supported Brett Kavanaugh’s confirmation to the U.S. Supreme Court.

Prosecutors sought an even longer sentence for Ronald DeRisi, saying he went to great lengths to mask his identity and researched the senators’ home addresses and personal phone numbers.

Sen. Chuck Grassley, of Iowa, has identified himself as one of the victims in the case. The staff of Sen. Susan Collins of Maine confirmed Monday to the Associated Press that she also received threatening messages from DeRisi.

Grassley served as chairman of the Senate Judiciary Committee when it advanced Kavanaugh’s nomination last year; Collins cast a decisive vote in Kavanaugh’s favor.

“Threatening to harm or kill elected officials because one disagrees with their public positions goes far beyond the scope of the First Amendment and will not be tolerated,” Brooklyn U.S. Attorney Richard Donoghue said in a statement.

DeRisi’s attorneys described him as an “angry, sick old man” who suffers from dementia but does not pose a risk of violence. They wrote in court filings that Kavanaugh’s nomination “sparked an inexplicable rage” in DeRisi, but that his physical condition made it “virtually impossible for him to carry out his threats.”

DeRisi, 75, of Smithtown on Long Island, pleaded guilty this year to making a series of threats that began the day before Kavanaugh appeared before the Senate Judiciary Committee for a highly anticipated hearing. Kavanaugh denied claims during the hearing that he sexually assaulted California psychologist Christine Blasey Ford.

In one of the threatening calls, DeRisi claimed to have a “present” for the senator, according to court filings.

“It’s a 9 mm,” he said, according to a criminal complaint.

DeRisi left 10 voicemails for another one of the senators beginning Oct. 6, the day Kavanaugh was confirmed by the U.S. Senate. In one of those messages, prosecutors said, Derisi referred to Kavanaugh as a sex offender and warned, “I’m gonna get you.”

Derisi made the calls from a pre-paid cellphone that that he hid in his car, prosecutors said. Investigators used cellphone records and location information from a phone provider to determine the calls were placed in the vicinity of DeRisi’s home in Suffolk County, according to the criminal complaint.

DeRisi previously pleaded guilty to making other harassing calls in a case that involved at least 15 calls he placed to a victim’s home and office, according to court documents.

Associated Press writers David Sharp in Portland, Maine, and Mary Clare Jalonick in Washington contributed to this report.

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