Staffers inside Donald Trump's own White House did not know of his plan to tap Matthew Whitaker as the acting Attorney General after firing Jeff Sessions and feel "a growing sense of concern" about the matter, CNN reports.

Whitaker is expected to take on oversight of the Robert Mueller probe despite the fact that he worked for one of the witnesses and has complained about the probe on conservative media. Whitaker had called Mueller's appointment as special prosecutor"ridiculous" and "a little fishy."

"It was not widely known among White House staff that he'd commented repeatedly on the special counsel's investigation in interviews and on television -- which is ironic given that this is what drew President Donald Trump to him and raises continued questions over the depth of the administration's vetting process," CNN reports.

The insiders said that the continued negative coverage of the appointment would get Trump's attention and jeopardize his future in the role.