Although authorities did not identify Proia’s target by name, describing her in a news release only as a “former political adviser and prominent member of the Republican Party,” two people familiar with the matter confirmed the alleged target was Katie Miller.

Prosecutors said Proia used an ever-changing series of phone numbers to contact Katie Miller at all hours, often using expletives and vulgar language to criticize her and her husband.

“The defendant repeatedly and relentlessly targeted the victim, her husband and her family with deeply disturbing communications that profoundly disrupted their lives,” said Leah Foley, the U.S. attorney in Massachusetts.

Proia was arrested Thursday by the FBI’s Joint Terrorism Task Force and was released after an initial appearance in federal court. His attorney did not immediately return requests for comment.

Katie Miller thanked Foley, Attorney General Todd Blanche, and the FBI’s Washington field office in a post to social media about the arrest.

Proia’s indictment follows days of internal Justice Department debate over the case. Last week, the FBI transferred the top two agents running the counterterrorism division of its Washington field office over dissatisfaction with what higher-ups deemed to be the slow pace of their investigation into the threats against Katie Miller, The Washington Post has reported.

As President Donald Trump’s policies — including an immigration enforcement crackdown in which Stephen Miller has played a prominent role — have provoked fierce opposition across the country, the administration has prioritized prosecuting people who threaten public officials, federal agents and judges. Administration officials have pointed to recent high-profile incidents of political violence, like the assassination of conservative activist Charlie Kirk last year, to justify their heightened vigilance.

In some cases, those threats have prompted indisputably serious concerns from federal investigators that the perpetrator intends to commit an violent acts.

But in many others, defense attorneys have objected to the Justice Department’s decision to label threatening messages “domestic terrorism” and questioned its expanding definition of what constitutes a threat worthy of federal prosecution instead of one better left to local authorities.

Several defendants who have been charged in recent months are accused of little more than making vaguely menacing posts online, with little evidence to suggest they had any intent or ability to act on those alleged threats.

Earlier this year, the Justice Department charged former FBI director James B. Comey with threatening the president’s life after he posted a photo to social media depicting seashells spelling out “86 47.” Trump is the 47th president and “86” can mean to get rid of someone. Prosecutors say it is also mob slang for killing someone.

Comey maintains he did not create the shell arrangement and had no idea it could be read as a threat.

But unlike Comey and others who have been charged under a statute that prohibits communicating interstate threats — which requires prosecutors to prove the message contained a threat of injury or violence — Proia was indicted under a cyberstalking statute that requires only proof that the defendant intended to harass their victim and attempted to cause substantial emotional distress.

Prosecutors said Thursday that the relentless nature of Proia’s alleged communications instilled “real fear and harm.” In one message, cited by authorities, he purportedly contacted Katie Miller’s parents referring to Stephen Miller as a “Jewish Nazi/white supremacist.”

“Did you raise her to be trash or did that just happen naturally?” Proia allegedly texted them.

The Millers have emerged as frequent targets. Last year, the couple and their children moved to housing at a secure military facility, citing concern for their personal safety following protests in the Arlington neighborhood where they were previously residing.

Local activists posted fliers disclosing their home address and scrawled messages on sidewalks in chalk accusing Stephen Miller — the architect of controversial White House policies on immigration enforcement and domestic terrorism — of “destroying democracy.”

“If we don’t step up and start putting people in cuffs for these actions, what comes next?” Katie Miller asked in a Fox News interview shortly afterward.

In May, Virginia prosecutors declined to bring a case against Barbara Wien, a retired peace studies professor, who was involved in those protests, saying she was “not likely to be found guilty and her speech [was] likely to be found constitutionally protected.”

The FBI’s Washington field office was also involved in that investigation, but to date no federal charges have been filed.

Perry Stein contributed to this report.