An explosive device was sent to CNN's NY offices on Wednesday, hours after authorities said they had intercepted suspicious packages intended for former U.S. President Barack Obama, and former Democratic presidential candidate Hillary Clinton.
A police bomb squad removed the package addressed to Mr Brennan from CNN's NY office, which was evacuated.
Two packages were sent to Waters, who Trump has called "an extraordinarily low IQ person".
Investigators are now working outside Washington, D.C., in NY, in Florida and in Los Angeles - where one of Waters' packages was found - to determine who sent the envelopes and why.
So why De Niro?
First lady Melania Trump said in a statement that, "Mrs. Trump condemns all forms of threats and violence" and "thanks law enforcement for their heroic efforts".
This comes as crude pipe bombs targeting Hillary Clinton, former President Barack Obama, CNN offices in NY and others were intercepted Tuesday night and Wednesday.
Investigators say it appears to be from the same sender.
NY police are investigating a suspicious package addressed to the actor De Niro and sent to his Tribeca property Thursday morning.
The parcel intended for Holder ended up rerouted to the return address printed on all the packages - the Florida office of U.S. Representative Debbie Wasserman Schultz, a former chair of the Democratic National Committee, according to the Federal Bureau of Investigation.
"Stop blaming others. Look in the mirror".
The report came a day after suspicious parcels were sent to Barack Obama, Hillary Clinton and other prominent Democrats. Former CIA Director turned anti-Trump TV pundit John Brennan went a step further, saying that Trump "has helped to incite some of these feelings of anger, if not violence, when he points to acts of violence or also talks about swinging at somebody from the press, the media".
"New Yorkers have never succumbed to fear or intimidation, and today will be no different", Cuomo said.
None of the suspect devices have gone off and the FBI are investigating who sent them.
Video: Authorities continue to investigate additional suspicious packages containing explosives that seem to target prominent liberal figures and Democratic politicians the week of October 22. It was addressed to Robert De Niro and is similar packaging to the others.
The first crude bomb to be discovered had been delivered on Monday to the suburban NY compound of George Soros, a liberal billionaire and major contributor to Democratic causes.
The package addressed to Holder did not reach him at his law firm in Washington, D.C.; instead it was rerouted to the return address affixed on the envelope - that of Florida Rep.
Maxine Waters: The US representative said in a statement that Capitol Police informed her that her Washington, DC office was a target of a suspicious package on Monday. Trump also often singles out CNN as he rails against the "fake news" media. Democratic House and Senate leaders Nancy Pelosi and Chuck Schumer both said that conciliatory talk sounds "hollow" coming from Trump.