Protesters rally for Robert Mueller

(NBC) - As the dust starts to settle from Wednesday's firing of U.S. Attorney General Jeff Sessions, many questions still hang in the balance surrounding the man President Trump chose to replace him.

Rallies were held across the country Thursday as Matt Whitaker began his first day on the job.

Critics believe he's biased against Robert Mueller, and should not be able to oversee the Russia investigation. Whitaker has been openly critical of the probe, and has even suggested how to shut it down.

"That Attorney General doesn't fire Bob Mueller, but he just reduces his budget so low that his investigation grinds to almost a halt," Whitaker said while working as conservative commentator for CNN in 2017.

The White House says there's no reason for Whitaker to recuse himself from the investigation, just like Jeff Sessions did last year.

Democrats are asking the White House and law enforcement officials to make sure records from Mueller's probe are not destroyed.