Muller sent a list of questions to Trump to review, in an effort to get the President to live up to his statements that he wants to sit down with the investigators for an interview. Worth noting that they were leaked after being provided to the President... it seems like the White House is a sieve.
In spite of angry tweets to the contrary, the questions do not paint a vague or distant picture of what the investigation is looking into. I'm sure Trump's legal team recognizes this, I'm not Sure the President understands the implicit Threat in the questions or he'd probably SLOW DOWN the twitter Fingers (random capitalization because I just Read Trump tweets and it Felt appropriate).
A sampling:
What did you know about phone calls that Mr. Flynn made with the Russian ambassador, Sergey I. Kislyak, in late December 2016?
After the resignations, what efforts were made to reach out to Mr. Flynn about seeking immunity or possible pardon?
What did you mean when you told Russian diplomats on May 10, 2017, that firing Mr. Comey had taken the pressure off?
What was the purpose of the September and October 2017 statements, including tweets, regarding an investigation of Mr. Comey?
Did you discuss whether Mr. Sessions would protect you, and reference past attorneys general?
What discussions did you have regarding terminating the special counsel, and what did you do when that consideration was reported in January 2018?
When did you become aware of the Trump Tower meeting?
What involvement did you have in the communication strategy, including the release of Donald Trump Jr.’s emails?
During the campaign, what did you know about Russian hacking, use of social media or other acts aimed at the campaign?
What knowledge did you have of any outreach by your campaign, including by Paul Manafort, to Russia about potential assistance to the campaign?
What did you know about communication between Roger Stone, his associates, Julian Assange or WikiLeaks?
What did you know during the transition about an attempt to establish back-channel communication to Russia, and Jared Kushner’s efforts?
What do you know about a Ukrainian peace proposal provided to Mr. Cohen in 2017?
https://www.nytimes.com/2018/04/30/us/politics/questions-mueller-wants-to-ask-trump-russia.html