Washington (CNN) The man taking over the Justice Department following Jeff Sessions' firing as attorney general has argued that special counsel Robert Mueller's investigation went too far.

Matthew Whitaker, who was Sessions' chief of staff, is expected to take over oversight of Mueller's investigation into Russian interference in the 2016 election and whether Trump campaign associates colluded with Russia. A source close to the President told CNN that the idea of Whitaker ending or suppressing the Russia probe is not an option as of now.

Trump's dismissal of Sessions has raised yet more questions over how much influence the President will have over Mueller's probe, which has been a source of pain since it began in spring 2017. Trump has complained repeatedly about Mueller's investigation, calling it a "witch hunt," and slammed Sessions in public repeatedly for recusing himself from the Russia probe, a step that helped lead to Deputy Attorney General Rod Rosenstein appointing Mueller.

In a CNN op-ed written last year, Whitaker argued that Mueller is "dangerously close to crossing" a red line following reports that Mueller was looking into Trump's finances.

He argued that Mueller does not have "broad, far-reaching powers in this investigation," but that the investigation's limits are clearly defined by Deputy Attorney General Rod Rosenstein's May 2017 letter appointing Mueller

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