Excellent article by Ambassador @dougkmiec: How Trump could stop the Russia investigation on constitutional grounds
http://www.latimes.com/opinion/op-ed/la-oe-kmiec-mueller-is-unconstitutional-20170727-story.html
There seem to be constitutional grounds, and also the enormous conflicts of interest of Mueller, Rosenstein and Mueller's hirelings.
Someone in the WH really needs to pull together the best legal experts they can find and brain storm all the possibilities of undoing this string of questionable decisions.