[mairdie]

https://www.dailymail.co.uk/news/article-7181851/Mueller-agrees-testify-Congress-month-PUBLIC.html

Robert Mueller agrees to testify about the Russia investigation before Congress in PUBLIC on July 17 after answering a subpoena from top Democrats – and Trump calls it ‘Presidential Harassment’

[TruthWillWin]

Robert Mueller agrees to testify about the Russia investigation before Congress in PUBLIC on July 17 after answering a subpoena from top Democrats – and Trump calls it ‘Presidential Harassment’

So that's what his tweet was all about.