Ryan Routh, 58, was already facing two gun-related charges after authorities said he pointed a rifle through a fence at Trump's golf club in West Palm Beach, Florida on September 15 while the Republican presidential candidate was golfing there. He has been ordered to remain in jail to await trial.
A federal prosecutor said on Monday that the US Justice Department would ask a grand jury to approve the more serious attempted assassination charge, which carries a maximum of life in prison.
US Attorney General Merrick Garland on Tuesday called the attempted assassination a "heinous act" and said the Justice Department will "spare no resource " on the case.
US Attorney General Merrick Garland vowed to "spare no resource" on the case. (EPA PHOTO)
Routh has not yet entered a plea. His lawyers unsuccessfully sought to have him released on bond.
Prosecutors have in recent days revealed evidence they said pointed toward a plan to kill Trump. They alleged that months before the incident, Routh dropped off a letter to an unidentified person alluding to "an assassination attempt on Donald Trump."
They said Routh spent a month in South Florida and mobile phone data showed him near the golf course and Trump's Florida residence at Mar-a-Lago. He was found with a handwritten list of dates and venues where Trump spoke or was expected to appear, according to court filings.
A US Secret Service agent searching the golf course ahead of Trump opened fire after discovering the gun poking through the fence, causing Routh to flee, prosecutors said. He was arrested within an hour along a Florida highway.
Routh was initially charged with possession of a firearm as a convicted felon and possession of a firearm with an obliterated serial number.
