A man arrested at a Donald Trump rally is facing federal charges after allegedly trying to grab the gun of a police officer for the purpose of trying to kill the GOP presidential candidate.

Michael Sandford, a British citizen, was arrested at Mr. Trump’s Las Vegas rally Saturday afternoon at the Treasure Island Casino after an altercation with a Las Vegas Metropolitan Police officer.

Mr. Sandford approached the officer, saying that he was trying to get an autograph from Mr. Trump, according to a charging document filed in federal court. He then proceeded unsuccessfully to try to seize the officer’s gun.

After his arrest, Mr. Sandford told the Secret Service that he had been plotting to kill Mr. Trump for about a year, according to the charging document. Mr. Sandford also told agents that he had visited a gun range in Las Vegas the day before the rally to learn how to use a weapon.

According to the Secret Service, Mr. Sandford had driven to Las Vegas from California for the purpose of killing Mr. Trump.