Acting Attorney General Matthew Whitaker, who took charge of the Justice Department after Jeff Sessions resigned Wednesday, criticized special counsel Robert Mueller's investigation into President Trump's alleged ties to Russia last year.

Whitaker, who served as Sessions’ chief of staff, outlined his criticisms of the Mueller probe in an August 2017 opinion article, shortly before he rejoined the department.

Mueller’s investigation has been overseen by Deputy Attorney General Rod Rosenstein, after Sessions recused himself last year when inconsistencies emerged about his congressional testimony about Trump campaign contacts with Russia.

Sessions' recusal infuriated Trump, who has repeatedly referred to Mueller's probe as a "witch hunt." On that point, the acting attorney general appears sympathetic, as he wrote that "the president is absolutely correct" to question Mueller's authority.

“It is time for Rosenstein ... to order Mueller to limit the scope of his investigation to the four corners of the order appointing him special counsel,” Whitaker wrote last year.

“If he doesn't, then Mueller's investigation will eventually start to look like a political fishing expedition. This would not only be out of character for a respected figure like Mueller, but also could be damaging to the president of the United States and his family — and by extension, to the country,” the former U.S. attorney for southern Iowa wrote.

Whitaker also argued that Trump's finances, those of his family, and those of his business should off-limits to Mueller.

“The Trump Organization's business dealings are plainly not within the scope of the investigation, nor should they be,” Whitaker wrote, also declaring that “[a]ny investigation into President Trump's finances or the finances of his family would require Mueller to return to Rod Rosenstein for additional authority under Mueller's appointment as special counsel.”

Mueller’s investigation has featured former Trump campaign manager Paul Manafort and deputy Rick Gates pleading guilty to pre-election crimes relating to foreign lobbying work, and former Trump personal attorney Michael Cohen pleading guilty to campaign-finance and financial crimes linked to Trump paying off porn star Stormy Daniels.

"It does not take a lawyer or even a former federal prosecutor like myself to conclude that investigating Donald Trump's finances or his family's finances falls completely outside of the realm of his 2016 campaign and allegations that the campaign coordinated with the Russian government or anyone else. That goes beyond the scope of the appointment of the special counsel," Whitaker wrote.