WASHINGTON — Former CIA Director John Brennan has been subpoenaed to testify before a federal grand jury in Fort Pierce, Florida, as part of a Justice Department investigation into whether officials who investigated Donald Trump conspired to violate his civil rights, Brennan’s attorney said Monday. The subpoena was delivered last Thursday and requires Brennan to appear Oct. 15. His lawyer, Ken Wainstein, disclosed it while asking U.S. District Judge Jia Cobb to order the Justice Department to preserve records related to the investigation. Wainstein said the inquiry involves a broad theory covering government investigations of Trump, including the probe into Russian interference in the 2016 election and the case involving classified documents found at Trump’s Mar-a-Lago estate. He said Brennan was among several people recently subpoenaed. Brennan is also the target of a separate investigation into whether he made false statements to Congress about the intelligence community’s assessment that Russia interfered in the 2016 election to benefit Trump. Brennan and his attorneys deny the allegation. Grand jury subpoenas issued in that false-statements inquiry last spring were later withdrawn, according to Wainstein, who said prosecutors instead sought voluntary interviews. The developments have intensified concerns about the Justice Department’s pursuit of a former intelligence chief who has been an outspoken critic of Trump. Wainstein argued that records showing direction from Trump or White House officials could help Brennan challenge any future prosecution as vindictive or selectively enforced. “There’s no precedent for this situation,” Wainstein told the court, saying he had never encountered what he characterized as an effort by the Justice Department to pursue someone for a crime he believes is fictional. He also alleged that the department had engaged in “judge-shopping” and that prosecutors who expressed doubts about the investigation had been replaced or resigned. The subpoena arrived the same day Joe diGenova, the prosecutor who had been leading the investigation, resigned. A person familiar with the matter said the departure followed frustration within the Justice Department and the White House over the pace and management of the inquiry. DiGenova disputed criticism of his work, saying there was sufficient evidence to support the investigations but that prosecutors needed time to develop the cases. The Justice Department has not announced who will replace him. Wainstein said the prosecutor with whom he spoke was Kurt Olsen, an attorney who unsuccessfully urged the Justice Department in 2020 to support Trump’s false claims that the presidential election had been stolen. The Justice Department opposed Brennan’s records request, calling it premature and speculative. Prosecutors also argued that Brennan, who has not been charged, has no legal right to demand preservation of government records for a possible future defense. Judge Cobb had not ruled on the request as of Monday. The grand jury proceedings are expected to remain secret unless prosecutors seek an indictment or other court action becomes public.