He was involved in the campaign which was being investigated. If he continued, he would be presiding over his own investigation. I think if a similar situation had been repeated but with the Obama campaign, you'd most likely see the conflict in the AG presiding over investigating himself. I think he thought he would lose a challenge in court that he should be recuse. I'm not sure that's true. It was a judgement call, and his actions are justified by the circumstances. Well. Unless you want the AG to be Trump's wingman. Maybe you can justify that position but I can't having spent too much time criticizing Holder for being Obama's wing man.
Who was the last AG that didn't function as the president's wingman?
This intentional self knee-capping just comes off as ego stroking rather than actually standing up for values.
It'd be like if congressional republicans refused to use the nuclear option because of some moral conflict, while democrats pass every bill they want using the nuclear option.
Pandora's box was already opened.
You can of course dislike it, and vocally detest it, while also understanding that you didn't create the game nor the rules, you're just playing to win it.