He was brought in by Comey to Counterintelligence division, just before the Carter Page FISA warrant was issued. (After the broader warrent for the Trump campaign was rejected). So McGonigal came in just 2 weeks before the Page warrant.

Then in March 2017 he expressed concern that Page warrant application could leak to public.

The Russia Sanctions that he is pleading guilty to right now, has to do with his contact with Deripaska - the guy they used as a witness against Trump campaign during that time. Willing to bet that he was the guy who propped him up, bribed/cajoled/forced him - and in the process violated the very same sanctions they put in place to punish Russia for not playing ball with them.

From his wiki page

In 2016, McGonigal was named Section Chief of the Cyber-Counterintelligence Coordination Section of the Counterintelligence Division. On October 4, 2016, it was announced that McGonigal was named "Special Agent in Charge of the Counterintelligence Division for the New York Field Office", appointed by James B. Comey.

In March 2017, McGonigal expressed concern in a text message to then-FBI Deputy Assistant Director of the Counterintelligence Division Jennifer Boone that the surveillance warrant application on Carter Page could leak to the public after being presented to the United States House Permanent Select Committee on Intelligence.

McGonigal retired from the FBI in 2018.