Serving as Trump’s Attorney General, Sessions recused from the investigation into Russian election interference. himself per a Department of Justice regulation that disallows officials from investigating campaigns they were a part of.

As head of the FBI, Sessions explained that Department of Justice regulations required he do so. The rule in question states that DoJ employees cannot “participate in a criminal investigation or prosecution if he has a personal or political relationship with any person or organization substantially involved…or who would be directly affected by the outcome.”

After, Trump repeatedly attacked his Attorney General, demanding he reverse his recusal. Sessions ultimately resigned the day after the 2018 midterm elections.

Trump continued to attack Sessions after, especially amid Sessions’ 2020 candidacy for Alabama’s US Senator.

Business Insider – Jeff Sessions explains why he recused himself from Trump campaign-related investigations
Business Insider – Jeff Sessions says he has no regrets over recusing himself from the Russia investigation
The New York Times – Trump Asked Sessions to Retain Control of Russia Inquiry After His Recusal
The Hill – Trump attacks Sessions: A ‘total disaster’ and ‘an embarrassment to the great state of Alabama’