POTUS was under constant and public threat from the likes of McConnell, Graham, et al and leadership in the DOJ not to touch Sessions.
When you think about it, it’s pretty damn frightening.
I don’t know what made Sessions think he was irreplaceable. I do understand why he was to the coup plotters.
I guess it depends on how you look it at. Sessions was nuertered when he recused. Firing Rosenstein and/or Mueller would have been the bigger threat to Trump's presidency.