Former White House Press Secretary Ari Fleischer said Thursday he believes it's highly unlikely that President Obama did not know an FBI informant was in the Trump campaign. 

"We need to know why did it begin, who authorized it and what role did Barack Obama have. Did he know the FBI had informants there? I'll guarantee you the answer is yes. No FBI would put informants in another presidential campaign without permission from the White House, including the president," he said on "Outnumbered."

He said the FBI counterintelligence probe "spiraled out of control" after the Obama administration chose not to warn Trump about possible infiltration by Russia. 

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President Trump has insisted that the FBI placed a "spy" in his campaign, calling it the "one of the biggest political scandals in U.S. history."

Former FBI Director James Comey and former Director of National Intelligence James Clapper have pushed back on his claims, with Clapper saying that an informant would have been targeting the Russians, not Trump. 

FBI and Justice Department officials briefed bipartisan group of lawmakers known as the "Gang of 8" Thursday on classified documents related to the special counsel's Russia investigation, after meeting with two key House Republican lawmakers.

Fleischer emphasized that he favors a full investigation of Russia's meddling in the election, but the public needs answers on the FBI informant's role and other key details.  

"It is fraught with risk when you put informants into an opposing political campaign," he explained. 

Watch the full discussion above. 

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