Story highlights Trump announced the proposal after accepting the endorsement of the New England Police Benevolent Association

Trump did not explain the legality of mandating a death penalty sentence via executive order

Portsmouth, New Hampshire (CNN) Donald Trump announced Thursday that if elected president, he would sign an executive order to mandate the death penalty for convicted cop killers.

Trump announced his latest legally questionable policy proposal after accepting the endorsement of the New England Police Benevolent Association, a police union representing more than 4,000 law enforcement officials -- an endorsement Trump characterized as a "lifetime improvement award."

"One of the first things I do, in terms of executive order if I win, will be to sign a strong, strong statement that will go out to the country -- out to the world -- that anybody killing a policeman, policewoman, a police officer -- anybody killing a police officer, the death penalty. It's going to happen, OK?" Trump said in brief remarks to the several hundred police union members gathered for the endorsement.

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Trump did not explain the legality of mandating a death penalty sentence via executive order. Nineteen states, as well as the District of Columbia, have outlawed the punishment. The death penalty is legal at the federal level and prosecutors can seek capital punishment in some murder cases, including ones involving the killings of state or local law enforcement officials, but it's unclear how an executive action could be used to require this.

Trump's campaign did not immediately return a request for comment.

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