Donald Trump promised, when elected president, to establish a “special prosecutor” to investigate Hillary Clinton, because “there has never been so many lies, so much deception.”

ST LOUIS, MO - OCTOBER 09: Republican presidential nominee Donald Trump looks at Democratic presidential nominee former Secretary of State Hillary Clinton during the town hall debate at Washington University on October 9, 2016 in St Louis, Missouri. This is the second of three presidential debates scheduled prior to the November 8th election. (Photo by Saul Loeb-Pool/Getty Images)

Republican presidential nominee Donald Trump looks at Democratic nominee Hillary Clinton during the town hall debate at Washington University on Oct. 9, 2016, in St. Louis, Missouri.

Photo: Saul Loeb/Getty Images

Clinton responded that it is “awfully good that someone with the temperament of Donald Trump is not in charge of the law in our country.”

Trump then explicitly threatened to jail her if he wins.

“Because you’d be in jail,” he said.

The FBI investigated Clinton’s private email server and did not recommend bringing any criminal charges.

Trump’s threat to jail the leader of a would-be opposition party is disturbingly reminiscent of a collapsing, unstable democracy, where an executive can direct the criminal justice system to jail whom he sees fit.