Not to say that Mueller can't have him framed, but even that is a long shot because Obama couldn't get rid of him even after having the U.S. and UK IC spy on Team Trump probably going back to the early "birther" days.
The target doesn’t actually seem to be Trump, from a legal standpoint. Probably Manafort and Flynn. Possibly even the leaker/hacker of DNC emails.
Though impeachment is exclusively a political decision, there has always been proof of crimes and actual convictions before the president is targeted directly.