The argument given for non-recusal isn't evidence-based, it's that the investigation was a spy investigation, not a criminal one. DOJ is for criminal stuff.
Given the forces aligned against the Trump administration, from inside DOJ, inside FBI, inside Congress, the press ... Sessions was toast from the get-go.
-- Sessions could have stopped this all in early 2017. Shut it down. --
Maybe. It would have taken a bit of foresight because he was asked about recusal during his confirmation hearing. Durbin was in on the scheme. Sessions didn't commit to recusing if the issue was Trump campaign.
At any rate, I view sessions as an honest man in the middle of a fundamentally dishonest government. Everybody in his orbit was gunning to take him out. Heck, years later, and the system is STILL tilted against Trump. Wray has been hiding evidence, the Senate has been passive aggressive against Trump, the House has been obsessed (thanks to Ryan, et al for ceding the House to the DEMs). Barr, who has substantial cache, is barely able to get candle-light on the subject.
"The only thing necessary for the triumph of evil is for good men to do nothing"
Sessions did nothing.
Nonsense. The DOJ does espionage cases too. The bring cases on any and all Federal laws.