Key Mueller witnesses: He's probing Russian collusion

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MSNBC Chief Legal Correspondent, Ari Melber, brings together four witnesses involved in Bob Mueller’s Russia probe. Former Trump Campaign aide, Sam Nunberg, says “one of the first questions” Mueller asked him, was “how often” Donald Trump himself spoke to Roger Stone. Nunberg says he believes the Mueller probe’s investigation of Trump campaign contacts with Russia during the 2016 election extend to Trump himself.