Gianforte pleaded guilty to that incident.
Hillary Clinton was not at her NY home when Tuesday's package was sent, but her husband, former President Bill Clinton was present, officials told the Associated Press.
Two packages were sent to California Congresswoman Maxine Waters, the Federal Bureau of Investigation said.
Investigators could be seen early Thursday at the US Postal Service facility along Quigley Boulevard in New Castle, where the bomb squad deployed a robot.
According to WPIX, authorities responded to 375 Greenwich Street in Tribeca.
The FBI confirmed there was law enforcement activity at the USA mail facility in DE and aerial footage shot by NBC showed a heavy law enforcement response. FBI Public Affairs Specialist Dave Fitz told CNN agents were "responding with our law enforcement partners to a US Postal facility in DE".
Yesterday, The United States went into a nationwide panic after several bomb threats targeted a variety of different parties, including Michelle & Barak Obama, The Clinton home, and CNN's headquarters. All the intended recipients are Democrats.
President Trump addressed the deep political divide in the country, seeking to tone down the discourse.
However, authorities warn they might not have found them all yet.
Police have sent the package to a secure facility in the Bronx, New York Police Department Commissioner James O'Neill said on Twitter. "Those engaged in the political arena must stop treating political opponents as being morally defective".
"One of the biggest fears overnight into this morning is there are more bombs out there", Berman said.
But Democratic Senate and House leaders Chuck Schumer of NY and Nancy Pelosi of California said Trump's words "ring hollow". In the days leading up to the threatening mailers, Trump attended a rally in Montana where he praised Republican Rep. Greg Gianforte, who attacked a reporter last May.
All of the targets are frequently maligned by right-wing critics. The targeted Democrats have all been verbally targeted by Trump in the past, as has CNN, which he's slammed various times for delivering "fake news".
The return address for Mr. Biden's package, along with several others, was a Florida office of Rep. She is the former chairwoman of the Democratic National Committee who was accused by Clinton rivals of secretly helping the party's eventual presidential nominee.
It comes after 24 hours of chaos with up to nine suspicious parcels - some containing crudely built pipe bombs - intercepted before reaching targets including former US President Barack Obama, former Secretary of State and presidential candidate Hillary Clinton and Mr Obama's attorney-general Eric Holder. Debbie Wasserman Schultz, whose return address was on it.
"An explosive sent to CNN prompted the evacuation of the Time Warner Center in NY, but no one was hurt".
The package found at CNN was addressed to John Brennan, a fierce critic of Trump and a former director of intelligence under Obama.
News reports that the package en route to De Niro, a vocal Trump critic who recently hurled F-bombs at the president during an awards speech, was discovered at his Manhattan office building.