What mistake does the FBI contact make on the phone in Chapter 9?

The FBI agent makes a mistake when he confuses names. The reporters call him back to confirm.

Bernstein ended the conversation and gave a thumbs-up signal to Woodward. Then it came to him that the agent had said John, not Bob, Haldeman. At times, it seemed that everyone in Washington mixed up Bob Haldeman and John Ehrlichman—“the German shepherds,” “the Prussians,” “the Berlin Wall,” as they were called. The reporters could not let the confusion persist, however. Bernstein called the agent back.

“Yeah, Haldeman, Bob Haldeman,” he replied. “I can never remember first names.”