Matthew Whitaker, whom President Donald Trump named as his acting attorney general on Wednesday, privately provided advice to the president last year on how the White House might be able to pressure the Justice Department to investigate the president’s political adversaries, Vox has learned.

Whitaker was an outspoken critic of special counsel Robert Mueller’s probe before he became the chief of staff to Attorney General Jeff Sessions in September 2017. That has rightfully raised concerns that Whitaker might now attempt to sabotage Mueller’s investigation. But new information suggests that Whitaker — while working for Sessions — advocated on behalf of, and attempted to facilitate, Trump’s desire to exploit the Justice Department and FBI to investigate the president’s enemies.

In May 2018, President Donald Trump demanded that the Justice Department open a criminal investigation into whether the FBI “infiltrated or surveilled” his presidential campaign and whether Obama administration officials were involved in this purported effort. Trump, his Republican allies in Congress, and conservative news organizations — most notably Fox News — were making such claims and amplifying those of others, even though they offered scant evidence, if any, that these allegations were true.

Sessions, Rosenstein, and other senior department officials believed that if they agreed to Trump’s wishes, doing so would constitute an improper politicization of the department that would set a dangerous precedent for Trump — or any future president — to exploit the powerful apparatus of the DOJ and FBI to investigate their political adversaries. Those efforts, in turn, coincided with the president’s campaign to undermine Mueller’s investigation into whether the president’s campaign aides, White House advisers, and members of his own family colluded with Russian to help Trump win the 2016 election.