Fake news again. Nixon did something illegal. Firing Comey was not an illegal act. Period.
Many attorneys will disagree. Not only did he obstruct the investigation by firing Comey, his administration put false reasons for the firing into the public forum. Then after the Comrade fired Comey, he threatened he with his Tweets about tapes that were not there.
But Mueller sees something bigger there and that is why Mueller is putting experts in money laundering and racketeering on his staff. If there is nothing there, then Donald should relax, which he isn't.