The head of the F.B.I.’s New York office isn’t backing down. James E. Dennehy, a seasoned and well-regarded agent, sent a passionate message to his team this week, declaring it’s time to “dig in” as the bureau faces mounting pressure.

Dennehy’s email comes after several officials involved in the Jan. 6 Capitol attack investigations were forced out, stirring unease among F.B.I. staff. He described the situation as a “battle of our own,” emphasizing that good employees were being targeted simply for doing their jobs.

The Justice Department recently asked the F.B.I. to identify personnel connected to the Jan. 6 probe, sparking fears of a broader purge. With around 6,000 employees potentially affected, morale at the bureau has taken a hit.

Dennehy, who leads the agency’s largest and most critical field office, urged his team to stay steady. He assured them he’d provide support no matter what happens. “Time for me to dig in,” he wrote, signaling his determination to stand by his colleagues.

In a rare move, Dennehy also praised the F.B.I.’s interim leaders, Brian Driscoll and Robert Kissane, for fighting to protect employees from abrupt removals. Their efforts to slow down the process have provided some relief during a chaotic time.

As the F.B.I. navigates this challenging period, Dennehy’s message serves as a rallying cry for agents to stay united and focused on their mission.