Fox News legal commentator Andrew Napolitano questioned the reasoning behind President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE's ouster of Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE on Wednesday, saying that Trump's move looked to be a first step in an attempt to end the Russia investigation.

Acting Attorney General Matthew Whitaker, who has sharply criticized special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE's probe in the past, will take over the job of overseeing the investigation, the Justice Department announced.

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“This is being done by a person who said, ‘Let’s dry him up by shrinking his budget.’ Beginning to look more and more to me, Shep, nefarious," Napolitano said in an interview with Fox News's Shepard Smith.

“The president can fire an attorney general for almost any reason, but not for an improper purpose. He cannot fire him if the purpose of the firing is to shake up the leadership of the Justice Department in order to interfere with a criminal investigation that the president wants to interfere with," the former judge added.

"[Whitaker] told CNN … that the best way to take care of Mueller is to dry up his funds," Napolitano continued. "If that is the reason for which Mr. Whitaker is now the acting attorney general of the United States, Mr. Whitaker himself could be in the crosshairs of Bob Mueller.”

Trump had been expected to seek a new attorney general after the conclusion of Tuesday's midterm elections, but the abrupt timing of Sessions's ouster caught many in Washington by surprise.

"We are pleased to announce that Matthew G. Whitaker, Chief of Staff to Attorney General Jeff Sessions at the Department of Justice, will become our new Acting Attorney General of the United States. He will serve our Country well," Trump said on Twitter.

"We thank Attorney General Jeff Sessions for his service, and wish him well! A permanent replacement will be nominated at a later date," the president added.