The top agent at the F.B.I.’s New York City field office vowed in a defiant email to his staff to “dig in” after the Trump administration targeted officials involved in the investigations into the Jan. 6 attack — and praised the bureau’s interim leaders for defending its independence.“Today, we find ourselves in the middle of a battle of our own, as good people are being walked out of the F.B.I. and others are being targeted because they did their jobs in accordance with the law and F.B.I. policy,” wrote James E. Dennehy, a veteran and highly-respected agent who has run...