A man in federal prison for threatening to kill past presidents was sentenced to an additional four years on Monday after he admitted to sending more death threats targeting high-ranking officials.

Prison staff intercepted letters in June that Stephen Boykin tried to mail while he was incarcerated, which included death threats against Vice President Kamala Harris, former President Barack Obama, First Lady Michelle Obama, and Florida Gov. Ron DeSantis, federal prosecutors said. Boykin admitted that he planned to carry out his threats once he got out of prison, according to prosecutors.

“What the other have planned will in fact happen. THERE no if and buts about this. It will end the way my father always wanted it to end. Destruction.” Boykin wrote in one letter, according to court records.

The sentencing Monday comes amid a surge in recent months of threats against several groups, including government officials, jurors and minority groups. Most recently, Attorney General Merrick Garland warned on Monday of an alarming surge of threats against election workers.

Last year saw a record high number of federal prosecutions for making public threats, according to research from the National Counterterrorism Innovation, Technology, and Education Center at the University of Nebraska, Omaha, and Chapman University provided to USA TODAY.

Boykin tried to mail threats from prison

Prison staff found several threats made in letters that Boykin, 52, tried to mail in June, according to an affidavit filed in U.S. District Court for the Northern District of West Virginia.

Boykin wrote that he planned to go to Washington D.C. to “take matters into my own hands” and “finish what I started,” according to court documents. He said he was going to ensure President Joe Biden wins the next election by “getting rid of” of his opponents, the affidavit said, and named DeSantis and Harris as "candidates" he would target.

Other letters threatened a purported Assistant U.S. Attorney in South Carolina, where Boykin was last prosecuted.

"I am writing to let you know I will be home soon to finally get mine and the other revenge," Boykin wrote in a letter addressed to a "Maxwell Caution," who he identifies as a prosecutor. "I [guess] you can call yourself the walking dead cause that basically what you are."

Boykin was handed a 10-year prison sentence in March 2009 for writing and mailing death threats to the White House against former President George W. Bush, former Vice President Dick Cheney, and Obama, according to court records.

Surge in violent threats against elected officials

Threats of all types have risen across the nation in recent years, including against government officials, jurors and religious and ethnic minorities.

Last month, a Florida man was sentenced to 14 months in prison after he admitted to calling the U.S. Supreme Court and threatening to kill Chief Justice John Roberts. The Marshals Service said serious threats against federal judges rose to 457 in fiscal year 2023, up from 224 in fiscal 2021.

In September, the self-proclaimed leader of a white supremacy group admitted in a guilty plea that he threatened jurors and witnesses in the Pittsburgh Tree of Life synagogue massacre trial, the deadliest antisemitic attack in U.S. history. A Texas woman was arrested and charged last year for threatening to kill the Black judge who was overseeing federal charges against former President Donald Trump that accused him of trying to steal the 2020 election.

Contributing: Will Carless, USA TODAY