A man who authorities say staked out Donald Trump for 12 hours on his golf course in Florida, and wrote of his desire to kill him, was indicted on Tuesday on charges that he attempted to assassinate a major presidential candidate.

Ryan Wesley Routh had been initially charged with two federal firearms offences.

The upgraded charges reflect the justice department’s assessment that he methodically plotted to kill the Republican nominee, aiming a rifle through the shrubbery surrounding Mr Trump’s West Palm Beach golf course on an afternoon Mr Trump was playing on it.

Routh left behind a note in which he described his intention.