'Swatting' is when police are triggered by fake emergencies in order to harass opponents. Security forces rang the doorbell of Republican Nikki Haley.
Trump had recently publicly denigrated Haley, who continues to refuse to withdraw from the primary election campaign. The number of similar attacks and threats has increased sharply in the last two months, targeting both Trump's allies and rivals. Targets include people who have publicly opposed Trump, like Maine state Rep. Shenna Bellows. Judges and at least one prosecutor handling cases against Trump have also been targeted.