It sounds like Trump trusted Sessions’ judgment—the guy was to be Sessions’ Deputy, after all—and got burned.
You don’t have to use hyperbole, btw. Trump could have known quite a bit about Rosenstein. But would he have chosen him if Sessions hadn’t been pushing for him?
Maybe not.
Any responsible adult in that situation would realize that "the buck stops here" -- that is, with the person who had the ultimate responsibility to make the decision, regardless of who else was involved in the process.
I'm sure Donald Trump would have gone batsh!t crazy -- and rightly so -- if one of Trump Jr.'s real estate projects was running into trouble and the kid blamed all the problems on a deputy project manager.
That's the only way any responsible leader in an organization works. Otherwise, you end up in a situation where the chief executive rants for days about how ineffective one of his senior managers is, while everyone in the organization wonders why the lunatic doesn't just fire the guy.
Oh, wait a minute ...
LOL.