The attorneys general from Oregon and Washington have joined 16 of their Democratic colleagues in calling for Acting U.S. Attorney General Matthew Whitaker to recuse himself from overseeing Special Counsel Robert Mueller’s investigation into contacts between President Trump's 2016 campaign and Russia.

Related: With Attorney General Jeff Sessions Out, What Happens Next In The Justice Department?

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In a letter sent to Whitaker and Deputy Attorney General Rod Rosenstein on Thursday, the top state law enforcement officials said, “a reasonable person could question [Whitaker’s] impartiality in the matter.”

Whitaker has taken over from Jeff Sessions, who resigned Wednesday after months of pressure from President Trump to do so. Since his appointment, past comments Whitaker made about Mueller's investigation have been played regularly on some cable news stations.

In cities across the country Thursday — including in Eugene and Portland — protesters gathered over Sessions' ousting and concerns about what that could mean for Mueller's investigation.

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Hundreds of people gathered at Portland’s waterfront to criticize President Trump. Among them was U.S. Sen. Ron Wyden, D-Oregon.

“We’re here tonight with friends and neighbors and folks from one end of America to another to say that no one, no one, is above the law in America," Wyden told the crowd.

Whitaker has questioned Mueller's authority to investigate aspects of Trump’s election campaign and suggested how to end the investigation: by cutting its budget.

Whitaker told CNN in 2017 he could envision a situation where a new attorney general would "reduce (Mueller's) budget so low that his investigation grinds to almost a halt."

Thursday's letter to the Justice Department was signed by Oregon's Ellen Rosenblum and Washington's Bob Ferguson and their colleagues in Hawaii, Connecticut, the District of Columbia, Vermont, Rhode Island, North Carolina, California, New Jersey, Minnesota, Illinois, Delaware, New York and Massachusetts.

"You must be aware that your public comments criticizing Mr. Mueller’s investigation have been widely circulated," the attorneys general wrote to Whitaker. "At various opportunities — in print, on television, and through social media — you have suggested cutting the Special Counsel’s budget or limiting his authority to follow lines of inquiry."

The attorneys general also said Muller must have the "full authority to investigate and, if warranted, prosecute any violations of federal law."

They said Rosenstein has “ably supervised” the special counsel investigation to this point and should continue to do so.