Many of the republicans, including Sessions, saw Trump as a means to an end (SCOTUS, taxes). Many still covet that end above all else, but those numbers are thinning, though not as much as any notion of humanity would demand. These people are Machiavellian in the most literal sense; they will only bail ship once their goal is put in question. I think Session realized that sooner than many GOPers (it only came so soon because of his proximity to the orange spreading death); his ambitions weren't augmented by Trump, but rather put at risk. Sessions is clearly beholden to the echoes of racism and white power, but he's also made a career on law and order, and the notion of impeccable personhood; he was willing to lie about Russia (and his contacts with) right up until the point he was caught--his worldview, and any hopes of acting upon it, did not allow him to continue such a lie after being caught. (He is just like the anonymous Op-ed writer, and many others, whom have not quite. They do not relinquish power, though they admit their hold on it is immoral)