President Trump was verbally and emotionally abusive toward his former Homeland Security Secretary Kirstjen Nielsen as the two clashed over his immigration policy, according to a new book.

Trump consistently complained that Nielsen wasn’t doing enough to curb illegal immigration, according to the book A Very Stable Genius, which was obtained by the Guardian.

“In some instances, the volatile president was verbally and emotionally abusive toward Nielsen,” authors Philip Rucker and Carol Leonnig wrote. “‘Kirstjen, you’re just not tough enough,’ Trump would tell her. Trump complained Nielsen did not ‘look the part’ of homeland security secretary.”

“He made fun of her and believed that at about five feet four inches she was not physically intimidating. ‘She’s so short,’ Trump would tell others about Nielsen. She and Kelly would try to make light of it. Kelly would rib her and say, ‘But you’ve got those little fists of fury!’”

Nielsen, 47, left her post in April after 16 months leading the department.

A year before her departure, the book described a contentious meeting where Trump berated Nielsen for not shutting down the border as illegal border crossings increased. Nielsen told Trump the move was illegal.

Trump “harassed” Nielsen with angry phone calls for the rest of the year, sometimes at 5 a.m., the book said. He often called her after watching Lou Dobbs on Fox Business.

“The president would routinely call Nielsen to say a version of ‘Did you see Lou Dobbs? You’re totally fucking embarrassing me. This is my issue!’… Sometimes, Trump would refer to one of Dobbs’s proposals and say, ‘Kirstjen, just do it. Just do it.’ ‘But we can’t do it,’ Nielsen would explain, usually because whatever Dobbs had uttered on TV was against the law,” the book said.

[Read more: 'I spoke truth to power': Kirstjen Nielsen on why she resigned from the Trump administration]