Protesters chanted "lock him up" as Donald Trump gave a speech to mark Veterans Day in Madison Square Park in central New York.
", "Sexist in chief" and "Impeach Trump" had gathered close to Madison Square Park in downtown Manhattan.
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Mr Trump offered his support to Gold Star families, those have lost someone serving in combat as a member of the US military.
Mr Trump had also famously derided former Senator John McCain's service in the Vietnam War, saying: "He's not a war hero.
Last week, a judge ruled that Mr Trump had broken the law when he misused $2.82 million that the Trump Foundation raised to help veterans to fund his presidential campaign instead.
During his speech, Mr Trump acknowledged New York Mayor Bill de Blasio, saying: "Also with us is New York City Mayor Bill de Blasio. »