Washington DC - A California man charged with attempting to assassinate President Donald Trump at a White House press gala last month pleaded not guilty on Monday, US media reported.

Cole Allen (31) entered a not guilty plea during an appearance in a federal district court in the nation's capital, The Hill and other outlets said.

Allen appeared in court wearing an orange jumpsuit and handcuffs.

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He faces four charges in connection with the April 25 attack at the White House Correspondents' Association dinner at a downtown Washington hotel and potentially faces life in prison if convicted.

Allen is charged with attempting to assassinate the president, transportation of a firearm and ammunition across state lines with intent to commit a felony, using a firearm during a crime of violence and assaulting a federal officer.

According to prosecutors, Allen, a highly-educated teacher and engineer, traveled from his home in California to Washington by train carrying an arsenal that included a shotgun, a handgun, and numerous knives.

Allen never got close to Trump or the other guests attending the White House press dinner on a lower floor. The president was rushed out of the venue by Secret Service agents after gunshots were heard.

Allen was tackled and arrested by law enforcement almost immediately after charging through a security checkpoint with multiple weapons. A Secret Service officer fired multiple times at Allen but did not hit him.

The annual dinner draws Washington journalists, administration officials, celebrities, and entertainers.

Trump has traditionally boycotted the dinner but decided to attend this year.

It was the third alleged assassination attempt against the 79-year-old Trump in less than two years.