Morning Joe’s Mika Brzezinski responded to President Donald Trump’s Wednesday tweet resurrecting the conspiracy theory that Joe Scarborough was somehow behind the death of his staffer in 2001 when he was a congressman in Florida.

In a couple of tweets celebrating NBC News’ sacking of Matt Lauer, Trump wondered if MSNBC-parent NBC also would terminate “low ratings Joe Scarborough based on the ‘unsolved mystery’ that took place in Florida years ago?” adding, “Investigate!” Trump appeared to be referencing the 2001 death of an intern for then Florida Rep. Scarborough. The intern, who was found dead in an office, collapsed of an un-diagnosed heart condition and having hit her head on the side of a desk, causing a fatal blood clot, the local medical examiner determined at the time.

While Scarborough sat by her side, silent, Brzezinski told viewers:

“The president was tweeting yesterday about, among other things, a conspiracy theory about Joe being a murderer.”

“Today the president crossed another deeply disturbing line. With his attack on Joe, the chief law enforcement officer of the United States of America advanced a false conspiracy theory to intimidate the press and cause a chilling effect on the First Amendment. Joe and I are not intimidated, and his bizarre behavior contravenes both the Constitution and basic moral judgment. This is all we are going to be saying on the matter.”