US Attorney General Jeff Sessions was sacked on Wednesday after unrelenting criticism from President Donald Trump over his recusal from an investigation into Russia's role in the 2016 presidential race.
With Sessions out of the picture, Trump has selected someone who has expressed significant skepticism about Mueller's investigation, signaling the president could be pushing for an imminent end to it.
Mr Trump had repeatedly assailed him publicly for not taking a tougher approach to illegal immigrants, and accused him of protecting Robert Mueller's investigation into whether the Trump campaign colluded with Russians - an investigation that is also examining whether the president himself obstructed justice.
Whitaker previously served under the George W. Bush administration as U.S. attorney for Iowa's Southern District from 2004 to 2009.
His chief of staff, Matt Whitaker, will become acting attorney general.
‘Saudi sent experts to cover up murder’
Saudi Arabia's King Salman bin Abdulaziz Al Saud and Crown Prince Mohammed bin Salman in Riyadh , Saudi Arabia, December 13, 2017.
Last month, when President Donald Trump was asked by The New York Times if special counsel Robert Mueller would be crossing a line if he started investigating the finances of Trump and his family, the President said, "I think that's a violation".
He called for the Mueller investigation's scope to be narrowed. "Whitaker must assure the continued protection of the investigation immediately". He went on to say, "Our paramount view is that any attorney general, whether this one or another one, should not be able to interfere with the Mueller investigation in any way".
"He will serve our Country well", said Trump of Whitaker. "But when everybody sees what's going on in the Justice Department - I always put "justice" now with quotes".
A senior GOP congressional aide reaffirmed the previous position for GOP leadership that Trump should not fire Mueller. He is a conservative who has written op-eds in the past suggesting that the Mueller Investigation of Trump and the 2016 election has gone "too far", and has also run for elected office three times in the past, all times as a Republican.
He added that he was not surprised the House flipped to Democratic control.