Trump was referring to a dossier, presumably harmful to his reputation, compiled past year by a private investigator and paid for, in part, by Democratic presidential candidate Hillary Clinton's campaign team.
Trump seemed to reference a segment from the TV show "Fox & Friends", which the president watches and often praises. FBI CANNOT (after all of this time) VERIFY CLAIMS IN DOSSIER OF RUSSIA/TRUMP COLLUSION. The Facebook ads from a Russian troll imply that the Russian propaganda campaign of 2016 didn't favour either Donald Trump or Hillary Clinton in many instances.
Within minutes, Fox & Friends completed the circle by sharing the tweet with their audience. "And they used this Crooked Hillary pile of garbage as the basis for going after the Trump Campaign!"
"This attack on the Federal Bureau of Investigation is really unprecedented, and Republican leadership, if they want to demonstrate any loyalty, not to the president, but to the country and to our institutions, needs to step up and say stop it", said former Maryland Representative Donna Edwards.
Trump was referencing the unverified allegations that he had colluded with Russian intelligence before the USA election to sabotage Hillary Clinton's presidential campaign.
Trump's tweet might not really be any surprise though, seeing how he's been trashing the FBI, James Comey and Andrew McCabe quite a bit in recent weeks.
Washington D.C. based opposition research firm Fusion GPS arranged the dossier, which was originally funded by the Washington Free Beacon during the Republican presidential primary. After Trump secured the nomination, former British intelligence officer Christopher Steele was hired by contractors for the Clinton campaign to continue the research and compile information regarding Trump's deep ties to Russian Federation.