The Justice Department has appointed Joseph diGenova, a longtime ally and former campaign lawyer for President Trump, to lead an expanding criminal inquiry into former federal officials who investigated Mr. Trump. The move follows the removal of a senior career prosecutor in Miami who had overseen the case and reportedly objected to advancing part of the investigation. DiGenova will work in South Florida alongside the local United States attorney, another Trump loyalist.

Part of the inquiry is using a grand jury in Fort Pierce, Florida, where it would fall under Judge Aileen M. Cannon, who previously issued rulings favorable to Mr. Trump in the classified documents case. The arrangement has raised concerns that the department is embracing politically charged tactics and unusual staffing decisions to pursue what Trump allies describe as a 'grand conspiracy' case against his perceived enemies.

The most developed portion of the investigation appears to focus on whether John Brennan, the former director of the Central Intelligence Agency, lied to Congress about a 2017 intelligence assessment concerning Russian interference in the 2016 election. Prosecutors are examining discrepancies related to references to the Steele dossier in that assessment. A prior special counsel investigation had declined to bring charges against senior intelligence officials, but the new inquiry has broadened and includes additional subpoenas related to the earlier Russia investigation.