Cheryl Mills, among others, has been greasing the wheels of the Clintons’ secrecy machine for decades. Hillary Clinton explains her use of a private e-mail account and a secret server to conduct State Department business as a matter of “convenience.” But congressional investigators are almost as interested in the fact that two of her closest advisers, personal aide Huma Abedin and chief of staff Cheryl Mills, also had e-mail addresses on the secret server. Were they also interested in “convenience” or intent on shielding their work from public-record requests? For many years, the two women have served as Hillary’s inner-palace...