Mollie Hemingway of The Federalist, as a member of Bret Baier's Fox News panel this evening, said something very insightful about Mueller's report. She observed the usual practice in U.S. criminal proceedings is innocent until proved guilty.
Hemingway noted that Mueller turned this on its head by complaining he could not prove Trump innocent of obstruction. Americans don't normally have to prove innocence, prosecutors have to prove guilt and the default setting is "innocent."
It appears the only two things the President did to obstruct the Mueller investigation were (a) to complain about its pointlessness and political motivation (First Amendment protected), and to refuse to testify against himself (a Fifth Amendment issue) although he did answer written questions.