Former Clinton campaign communications director: Emails were 'a box we could never get out of'

"I think it was the unease people felt about Hillary's motivation as a woman seeking power that made it impossible for us to very fully put this matter to bed," Palmieri writes, according to the Post. "I have weathered a lot of political crises, but never encountered one quite like this."

In "Dear Madam President," which the Post describes as part recollection of the campaign and part guide for working women, Palmieri says the campaign's advice to Clinton not to forcefully address concerns about her use of a private email server while secretary of state actually differed from what Clinton believed she needed to do in the final days of the campaign.

"It was a mistake, although at the time it was hard to accept that telling Hillary to keep bringing up the emails herself could possibly be the right advice," Palmieri writes, according to the Post. "But I should have seen that, as unappealing as addressing the issue was, it was what voters needed to hear from Hillary at that moment. She got that."

During the 2016 election, Clinton faced heavy scrutiny for using a private email server for government work while running the State Department. At one point just before the election, then-FBI Director James Comey announced the agency would be reopening an investigation into the matter, which some -- including Clinton -- speculate cost her the election.