Friday's tweet marked the first time Mr Trump has publicly acknowledged he is under investigation. For perfectly understandable reasons, Trump wanted that question cleared up in the eyes of the public, and Comey - who seemed quite happy to leak just about anything and everything else - refused to set the record straight on that question.
The rising criticism puts a new focus on the relationships between the president, special counsel and the Justice Department, especially as questions loom over whether Deputy Attorney General Rod Rosenstein will recuse himself from overseeing Mueller's probe.
Rosenstein brought up the possibility of recusing himself during a meeting with the Justice Department's third-in-command - behind Sessions and Rosenstein - Associate Attorney General Rachel Brand, ABC News reported.
So far, Mueller's team does not look like a group of fair-minded, independent attorneys.
Sen. Dianne Feinstein, the top Democrat on the Senate Judiciary Committee, said she was "increasingly concerned" that Trump will fire both Mueller and Rosenstein. In that case, Rosenstein could be called as a witness.
The probe into Kushner's business dealings is part of the special counsel's investigation into Russia's interference in the 2016 presidential election.
Trump took to twitter on Friday to deny any involvement with Russian hackers during the 2016 presidential election and criticised an unnamed leader of the complex investigation that is consuming his White House.
When Trump fired former FBI Director James Comey last month, he initially cited a memo written by Rosenstein as the basis for the dismissal. The president complained the probe is unfair and wondered why his defeated Democratic opponent was not getting the same scrutiny.
USA intelligence agencies concluded in January that Russian Federation interfered in the presidential race to try to help Trump win, in part by hacking and releasing emails damaging to his Democratic opponent, Hillary Clinton. Pence's office confirmed he had retained Richard Cullen, a former Virginia attorney general and US attorney for the Eastern District of Virginia, to assist "in responding to inquiries" from Mueller. But before leaving, the president of the United States fired up Twitter, responding to reports he's under investigation for possible obstruction of justice. He is reportedly interviewing three top intelligence officials - Director of National Intelligence Dan Coats, National Security Agency Director Mike Rogers and retired deputy NSA director Richard Ledgett - as part of the probe as early as this week. During an interview with NBC two days later, Trump said he fired Comey because "this Russian Federation thing with Trump and Russian Federation is a made-up story". Rosenstein last month appointed former FBI Director Robert Mueller as special counsel overseeing the probe.
Flynn, dismissed by Trump in February after it emerged he had misled Pence about conversations with the Russian ambassador, is a subject in investigations by intelligence committees in the House of Representatives and Senate, as well as the FBI. Former President Bill Clinton met with Attorney General Loretta Lynch on an airport tarmac near the end of an investigation into Hillary Clinton's email server, but there's no evidence the former secretary of state orchestrated the get-together, as Trump implied.