"The Special Counsel, Robert S. Mueller III, is investigating tweets and negative statements by the President about Attorney General Jeff Sessions and former FBI Director James B. Comey, so three people who learned about it." HisSoapbox
Trump has said that without Twitter – and the ability to talk to him without cutting his followers – he may have won nothing.
As his term progressed, Trump was increasingly using his Twitter account. Feed to run his own kind of diplomacy. "North Korean leader Kim Jong Un said the nuclear button is always on his desk," Trump tweeted in January. "Anyone wanting to tell him about his exhausted and food starving regime that I have a nuclear button as well, but he is much bigger and more powerful than him and my button works!"
The constant through all this was Trump uses Twitter to complain about the investigation of the Ministry of Justice against Russia's interference in the 2016 elections – and everything from former FBI director James Comey to meetings and back with them brings. Trump is determined to call the investigation in Russia a "witch hunt" or a "hoax" for his entire presidency.
May 2017: 3 times
June 2017: 5 times  July 2017: 6 times
Oct 2017: 1 time
Dec, 2017: 2 times
Jan 2018: 1 time
Feb 2018: 3 times
March 2018: 2 times
April 2018: 9 times
May 2018: 20 times
June 2018: 26 times
The point: It's not clear if Trump's Twitter obsession – and his unwillingness to listen to his advisors when it comes to attacking members of his own Justice Department – will be his ruin. But we now know that the tweets are part of the wider Mueller probe.