Florida-based amateur bodybuilder Cesar Sayoc, who in March admitted to mailing crude bombs to prominent Democrats and critics of U.S. President Donald Trump, was sentenced to 20 years in prison by a New York court on Monday.

A fanatical Trump supporter, Sayoc sent 16 "improvised explosive device" to 13 intended victims including ex-president Barack Obama, former presidential nominee Hillary Clinton and former vice president Joe Biden ahead of the November 2018 midterm elections, according to prosecutors.

Others targeted by Sayoc included billionaire George Soros, former president Bill Clinton, and actor Robert De Niro. Several Democratic lawmakers, including 2020 presidential hopefuls Cory Booker and Kamala Harris, were also targeted.

None of the bombs exploded and no one was injured but the potentially deadly packages triggered nationwide panic and heightened political tensions in the lead-up to the midterm.

The 57-year-old one-time pizza delivery man who lived in a white truck plastered with pro-Trump and anti-Democrat stickers, broke down and wept as the sentence was handed down in a New York court.

"The nature and circumstances of the crimes are by any nature horrendous," said District Judge Jed Rakoff as he delivered the sentence.

The case has fueled a debate about extremism in the Trump era, which intensified at the weekend following two shootings that left 31 dead and dozens wounded in Texas and Ohio.

Critics say Trump's anti-immigrant rhetoric helps fuel white nationalist thinking that engenders violence. On Monday, the president said the US "must condemn racism, bigotry, and white supremacy."

Sayoc, who also once worked as a strip club DJ and bodybuilder, pleaded guilty in March to 65 charges relating to 16 package bombs he sent from a Florida post office to leading Democrats and the Manhattan offices of CNN.

Sayoc made the homemade devices from materials including plastic piping, a digital alarm clock with electric wiring attached, fireworks and glass fragments.

Dressed in a grey and blue checked blazer, shirt and tie, Sayoc read a statement to the court in which he said he was "beyond so very sorry for what I did."

"I will be apologizing to the victims for the rest of my life," he said.

Sayoc’s defense lawyers demanded minimum sentence of 10 years urging the court to show leniency. They argued that Sayoc was a troubled man who hit a breaking point after years of untreated mental health issues and steroid addiction as his life took a turn for the worse.

Estranged by family and living in abject poverty, Sayoc turned to spiritual candles and self-help books – including Trump’s writing, the lawyer said. "The books by Donald Trump really resonated with him," said defense lawyer Ian Marcus Amelkin. "Then he kind of became obsessed with Donald Trump."

Sayoc reportedly spent money on "Trump-branded" outfits, according to the lawyers. "He looked up to the president, as a father figure," Amelkin said. "He watched Fox News … he was expressing a lot of hateful ideas and conspiracy theories."

The steroids, meanwhile, fostered obsession with Democratic party figures, Amelkin said. "We believe that the president’s rhetoric contributed to Mr Sayoc’s behavior," he added.

Trump's inner circle initially attempted to distance the president from Sayoc until filmmaker Michael Moore released footage of the bomber attending a Trump rally, one month after the inauguration.

The martial arts practitioner was arrested in Florida in October five days after the first device was discovered in Soros's upstate New York mailbox. Police found Sayoc's fingerprints and DNA on the packages.

Prosecutors had called for life imprisonment for Sayoc arguing that he was aware of his actions and that 10 years would have been "wholly insufficient".

"The defendant created a climate of fear and terror," said prosecutor Jane Kim, later adding: "Politics cannot justify a terror attack."

Sayoc has a criminal record dating back to 1991, peppered with convictions for theft, fraud, violence and a threat to blow up his electric utility company.