WINSTON-SALEM, N.C. - President Trump isn't happy about a special counsel investigating his possible campaign ties to Russia.

He slammed the Justice Department's decision Thursday morning by tweeting – “This is the single greatest witch hunt of a politician in American history."

2 Wants To Know the last President to get a special counsel.

Wake Forest Professor Katy Harriger said it was during Bill Clinton's presidency. At that time, they called it an independent counsel.

They investigated the Whitewater scandal and the Monica Lewinsky allegations.

Harriger said a special counsel is usually brought it when the DOJ's response might not be viewed as reliable by the public.

“The independence is supposed to reassure us, whatever the outcome.” Harriger said. “Regardless of which outcome, the public is supposed to feel reassured that the investigation was done fairly.”

Harriger added that Special Counsel and Special Prosecutor are used interchangeably.

“Counsel just sounds a little more neutral because right now we’re just in the investigative stage.”