On Wednesday, Jeff Sessions resigned as the country's chief law enforcement officer.
Trump said on Friday, as he was departing Washington for a trip to Paris, that he had not discussed the Mueller probe with Whitaker before appointing him, and it was up to Whitaker whether he wanted to be involved with the investigation.
A spokesman for the panel's Republican chairman, Bob Goodlatte, declined to comment on the letter.
Hundreds of protesters have taken to the streets of major USA cities to call for protection of the special counsel charged with investigating ties between Russian Federation and President Donald Trump's 2016 election campaign.
That set off immediate alarm bells: Whitaker has been overtly critical of the broad scope granted to Mueller's team to probe beyond allegations Trump's campaign colluded with Russian Federation in 2016, into other ties between Trump, his family and aides, and Russian Federation - an investigation the president calls a "witch hunt". Assuming Justice Department ethics officials give Whitaker the green light (or he ignores a ruling that he should recuse himself) the acting Attorney General will likely take steps to rein in Mueller and his investigators. Rosenstein had the role of supervising the probe because of Sessions' recusal.
In a cosigned letter, the attorneys general said that Special Counsel Robert Mueller's probe "must proceed free from interference".
If he has found solid evidence, Mueller is not expected to indict the president, given the unsettled state of law on that course of action.More news: Google to overhaul sexual harassment policies following employee walkout
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"Therefore, Whitaker can not serve as acting Attorney General ..."
A replacement for Mueller though would have no such constraints, potentially allowing Trump to hamstring the investigators. The Senate Judiciary Committee already approved a bipartisan bill to do so in April.
Gonzales said if a decision is made to curtail or end the Mueller probe, that shouldn't be made by the acting attorney general, but someone within the normal lines of the chain of authority, either the deputy attorney general or the solicitor general.
Senator John Cornyn, the chamber's No. 2 Republican, has said he backs a non-binding resolution expressing support for Mueller.
As you can imagine, more people are reading The Jerusalem Post than ever before.
But their relationship has been complicated by the fact that Christie, while a US attorney in New Jersey from 2002 to 2008, convinced real estate developer Charles Kushner to accept a plea deal on corruption charges in 2004. At a news conference on Wednesday, the president threatened political warfare if Democrats exercise their new oversight power.
"Donald Trump wasted no time after the midterm elections interfering in the Mueller investigation", the statement said.