The packages stoked nationwide tensions and fears as voters prepared to vote Nov. 6 to determine partisan control of Congress — a campaign both major political parties have described in near-apocalyptic terms. Even with the sender still unknown, politicians from both parties used the threats to decry a toxic political climate and lay blame.
"A very big part of the Anger we see today in our society is caused by the purposely false and inaccurate reporting of the Mainstream Media that I refer to as Fake News," Trump said on Twitter. "It has gotten so bad and hateful that it is beyond description. Mainstream Media must clean up its act, FAST!"
Former CIA Director John Brennan, the target of a package sent to CNN, fired back.
"Stop blaming others. Look in the mirror," Brennan tweeted. "Your inflammatory rhetoric, insults, lies, & encouragement of physical violence are disgraceful. Clean up your act....try to act Presidential."
CNN didn't immediately respond to messages seeking comment before business hours Friday.
The list of bombing targets spread from New York, Delaware, and Washington, D.C., to Florida and California.
The explosive devices were packed in envelopes with bubble-wrap interiors bearing six American flag stamps and the return address of Florida Rep. Debbie Wasserman Schultz, the former chairwoman of the Democratic National Committee.
The bombs seized Wednesday were about 6 inches (15 centimeters) long and packed with powder and broken glass, according to a law enforcement official who viewed X-ray images. The official said the devices were made from PVC pipe and covered with black tape. At the New York briefing, authorities confirmed that at least some of the packages were distributed through the U.S. mail, and cautioned that there could be additional devices in the postal system. They said investigators searching for more suspicious parcels had not found any during the previous eight hours.
David Chipman, a retired federal ATF agent and now senior policy adviser for the Giffords Center, said the details revealed telltale signs that could help guide investigators.
The tape on the pipe is "an investigator's dream," he said, recalling a case in Texas that was solved because the fibers on the tape were traced to the bomber's dog. He said bombers tend to plot methodically.
"This is someone sitting down and spending time thinking about what they're going to do to someone else. And some people like to relish that," he said.
The new packages discovered Thursday set off a new wave of alarm.
A retired New York police detective working in security in De Niro's Manhattan office called police after seeing images of a package bomb sent to CNN and recalling a similar package addressed to the actor, officials said.
The packages addressed to Biden were intercepted at Delaware mail facilities in New Castle and Wilmington, according to a law enforcement official who, like others, wasn't authorized to discuss the investigation and spoke on condition of anonymity.
Like earlier targets, both Biden and De Niro have been sharply critical of Trump. The actor dropped an expletive insult at Trump at this year's Tony Awards and apologized to Canadians for the "idiotic behavior of my president." Biden said last week that the president may not "know what he's doing" and coddles dictators.
Trump has called Biden "Crazy Joe" and "mentally weak."
On Thursday, during a campaign trip to suburban Buffalo, Biden said: "We've got to get off this hate machine. We've got to come together."
The packages were "clearly an effort to terrorize people politically, to choose people for political purposes and attack them because of their beliefs," New York Mayor Bill de Blasio said.
The first crude bomb to be discovered was delivered Monday to the suburban New York compound of George Soros, a liberal billionaire and major contributor to Democratic causes. Soros has called Trump's presidency "dangerous."
Similar packages addressed to Clinton and Obama were intercepted on their way to Clinton's New York home, where she lives with former President Bill Clinton, and to Washington, where Obama lives with his wife, Michelle Obama. The Secret Service said neither package reached its intended recipient.
Other packages were sent to frequent Trump critics Waters, D-Calif., and former Obama Attorney General Eric Holder. His ended up at the Sunrise, Florida, office of Wasserman Schultz, who was listed as the return address.
A police bomb squad removed the package addressed to Brennan on Wednesday from CNN's New York office, which was evacuated.
In response to the events, Trump decried political violence but also joked about moving to more polite speeches.
"Let's get along," he said at a Wisconsin rally Wednesday night. "By the way, do you see how nice I'm behaving tonight? Have you ever seen this?"