Fox News senior judicial analyst Judge Andrew Napolitano revealed the critical question that must be answered following reports detailing how an FBI “informant” had multiple contacts with members of the Trump campaign.

The Justice Department on Sunday asked its watchdog to look into any "impropriety or political motivation" in the FBI's investigation of Russian interference in the 2016 election.

The move came hours after President Trump called for a review looking into whether federal agents infiltrated or surveilled his campaign for political purposes.

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On "America's Newsroom," Napolitano said the "$64,000 question" is: Was the informant sent by the intelligence community or the FBI?

He explained that if the informant was sent by the intelligence community, then his presence was "probably not criminal."

If the informant was sent by the FBI to gather evidence of crimes, however, then it's the equivalent of a search, Napolitano said, which means the bureau would need to justify it with evidence of crimes and a search warrant from a federal judge.

"If he was sent by the FBI without a search warrant, then President Trump is right. We have one of the greatest political scandals on our hands," Napolitano said, explaining that would raise questions about whether the Trump campaign was infiltrated and surveilled for political purposes.

"That's the fear. If that happened, it's the type of surveillance we have not seen or known about in modern American history."

He added that there's another critical question to be answered: "Where the heck was Barack Obama? What did President Obama know about this?"

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