Chase Bliss Colasurdo, 27, was arrested last May after he posted a photo on Instagram of a gun pointed at a picture of Jared Kushner, the president's son-in-law and adviser.
He pleaded guilty to threatening to bomb synagogues, hurt media members in Southern California and to making online threats to Kushner and Donald Trump, Jr.
Colasurdo was arrested after he bought a bulletproof vest and ammunition. He also tried to buy a gun but was denied after being flagged by the Secret Service.
He has a history of severe mental illness and paranoid delusions, authorities said.
U.S. Attorney Brian Moran said the case is a "frightening intersection of mental illness and weapons."