Transcript for Trump's pick for temporary AG faces possible legal challenge
Washington and growing fallout from president trump's firing of attorney general Jeff sessions. The president's temporary pick to replace him, Matthew Whitaker is facing calls to remove himself from the Russia investigation as the president considers permanent nominees for attorney general. Cecilia Vega tracking all the developments. Reporter: Before he was at the justice department, Whitaker was a conservative commentator means there is a long public record of all of his comments on all things Donald Trump and now those interviews on radio and television are coming to light and fueling these calls for his recusal. This morning, president trump's new acting attorney general is under fire for previously criticizing the very investigation he now oversees. Matthew Whitaker taking over at the department of justice after Jeff sessions was ousted in the hours after election day and now the one-time conservative commentator's past comments are coming back to haunt him. The truth is there was no collusion with the Russians and the trump campaign. Reporter: Last year Whitaker bashed Robert Mueller's Russia probe. There is thought a single piece of evidence that demonstrates that the trump complain had any illegal or even improper relationships with Russians. It's that simple. Reporter: On the question of collusion by president trump? If all he did was make a mere suggestion and not an outright command, I don't think that rises to the level of obstruction of justice. Reporter: He also called Mueller's appointment ridiculous and says it smells a little fishy. I hope it doesn't turn into a fishing expedition because I will be one of the ones jumping up and down making sure the limitations on this investigation continue because that's the way it's supposed to be. Reporter: He defended president trump. It is not helping this administration and really not helping the federal government generally to have the president and his associates under the cloud of a federal investigation. I mean, it is -- it is very hard. Reporter: Unlike sessions sources tell ABC news Whitaker will not recuse himself from overseeing the Russia probe. Something that has Democrats outraged. I think he has a clear conflict of interest in terms of overseeing any part of the Mueller investigation. Reporter: And it's not just on capitol hill. Overnight protesters around the country from New York to Chicago to the white house calling on Whitaker to step aside. But inside the white house sources tell ABC Whitaker is on the short list to permanently lead the justice department. That list also including at least a half dozen other political supporters like the president's personal attorney Rudy Giuliani, former New Jersey governor and current ABC news contributor, Chris Christie, senator Lindsey graham and Florida attorney general Pam Bondi. Now, it's not just Democrats sounding the alarm about Whitaker. A prominent conservative lawyer who also happens to be the husband of kellyanne Conway wrote an op-ed along with the former solicitor general under president Obama and say it's unconstitutional and anything Whitaker does in this position should be invalid. They want to see him undergo a senate confirmation hearing because they say there's been no scrutiny of his record. That could lead to a legal challenge. Meantime, on the search for a replacement, how quickly does the president hope to act? Reporter: We're hearing there is no real rush to get it done and may want until Mueller's investigation is finished. Thanks. It's been quite a week. You'll have a lot to talk about on "This week."
This transcript has been automatically generated and may not be 100% accurate.