The person in Florida was taken into custody after investigators responded to two suspicious devices on Friday, one of which was addressed to Sen.
A device destined for former Attorney General Eric Holder was instead sent to former Democratic National Committee Chair Debbie Wasserman Schultz, whose office was listed as the return address on numerous packages.
Prior to the arrest, Attorney General Jeff Sessions said on Friday that the Justice Department was dedicating every available resource to the investigation and "I can tell you this: We will find the person or persons responsible".
"We have confirmed this fingerprint is that of Cesar Sayoc", he said.
According to state voter registration records, Sayoc is a registered Republican who voted in the 2016 election.
He also has ties to NY and a criminal history.
A white van with numerous stickers on both sides and on the back was also seized in connection with the arrest in Plantation, Florida in Broward County, near Fort Lauderdale.
President Donald Trump discussed the investigation into the bomb packages at the Young Black Leadership Summit, at the White House, where he was already scheduled to speak. Authorities have not said whether the van is connected with Sayoc.
In the 2002 bomb threat case, Sayoc pleaded guilty to the felony without a trial and was sentenced to probation, the records show.
Similar packages addressed to Clinton and Obama were intercepted on their way to Clinton's NY home, where she lives with former President Bill Clinton, and to Washington, where Obama lives with his wife, Michelle Obama.
"I'm not suggesting a direct cause and effect relationship between anything he's said or done and these - and the distribution of these explosives", Clapper told CNN.
US Homeland Security Secretary Kirstjen Nielsen said Florida appeared to be the starting point for at least some of the bomb shipments.
The FBI said the package to Booker was intercepted in Florida. The most recent packages were intercepted on Friday in California, Florida and NY targeting Harris, Booker and former intelligence chief James Clapper, another prominent Trump critic.
Map showing the locations of packages across the U.S.
The series of bomb alerts began on Monday, when a suspected device was found in the post box of billionaire businessman George Soros, a major Democratic Party donor.
The common thread among the bomb targets was obvious: their critical words for Trump and his frequent, harsher criticism in return.
The @hardrock2016 account also sent threatening messages to people like Biden and Jim Carrey, according to The Daily Beast. He reprised the phrase "fake news" that he notably refrained from uttering on Wednesday at his previous rally in Wisconsin just hours after a mail bomb was delivered to CNN's studios in NY.