Michael Steven Sandford (20) said he had been planning to kill the US presidential hopeful for about a year
Michael Steven Sandford was detained on Saturday in Las Vegas after he allegedly tried to wrestle a gun from a police officer at the event.
The 20-year-old was then handed over to the US Secret Service, according to Las Vegas police.
He said he had driven to the city from California and was planning to shoot Mr Trump, according to court papers filed on Monday.
Sandford is reported to have a British driving licence and claims to have been in the US for around 18 months.
He has been charged with committing an act of violence on restricted ground, said US Attorney's Office spokesman Natalie Collins.
He appeared before Federal Magistrate Judge George Foley, who refused him bail.
Sandford, who wore leg irons and reportedly appeared to tremble during his court appearance, has not entered a plea.
He will reappear in court on July 5th.
Court papers say: "Sandford claimed he had been attempting to kill Trump for about a year but decided to act on this occasion because he finally felt confident about trying it."
The papers cite a Special Agent Swierkowski, according to US media, who said Sandford had arrived in New Jersey before ending up in the San Bernardino, California, area.
He reportedly told the agent he had driven to Las Vegas after seeing reports that Mr Trump would be holding an event there.
Sandford had arrived in Las Vegas on Friday and then went to a gun range to learn how to shoot a gun - something he told the agent he had not done before.