The second Presidential debate is now behind us and there’s a lot to discuss, but one issue stands out above the rest. It wasn’t the WikiLeaks revelation. It wasn’t Donald Trump calling Hillary Clinton “the devil.” It wasn’t Trump digging up old accusations of sexual misconduct against Bill Clinton, and it wasn’t even the leaked tape of Donald trump discussing sexually assaulting women.

No, every one of those issues, policy or personal, is secondary to a comment that Donald Trump made relatively early on in the debate.

While discussing Hillary’s email scandal Trump said, and this is a direct quote, “I’ll tell you what, I didn’t think I’d say this and I’m going to say it and hate to say it: If I win, I’m going to instruct the attorney general to get a special prosecutor to look into your situation because there’s never been so many lies, so much deception. Never been anything like it and we’re going to have a special prosecutor.”

Clinton responded by saying “it’s just awfully good that someone with the temperament of Donald Trump is not in charge of the law in our country.” Trump then said “because you’d be in jail.”

Let this sink in for a moment here. A nominee for President of the United States of a major political party, during a nationally televised live debate, announced that if he wins the election he will seek legal action against his opponent and will use his Justice Department to target her.

And if you think this was a fluke, some kind of offhanded comment, Trump’s campaign actually tweeted out a clip of that exchange on his official twitter account that night, and Trump doubled down on his promise to appoint a special prosecutor during a rally on Monday morning.

This is absolutely unprecedented. Donald Trump just threatened Hillary Clinton with prosecution and said that if he were in charge of the government she would be in prison. This is a first in the entire history of American political debates.

The terrifying thing is that this is not the first time this kind of dialogue has come up during the election. Chants of “lock her up” are commonplaces at Trump rallies around the country. During the Republican National Convention in Cleveland NJ Governor Chris Christie led a “witch-trial” like speech in which he led a mock show trial during which he rattled off a list of “charges” against Clinton and the crowd chanted “guilty” and “lock her up.”

This is something that just doesn’t happen in the United States. We have fair and open elections. We don’t lock up our political opponents. And we don’t threaten them with prosecution or criminal proceedings.

Dialogue like Donald Trump’s is reminiscent of a third world dictatorship, where people are jailed for speaking out against the party in power and authoritarian strongmen lock up their political opponents. America has always been different than that, and that difference is part of what makes America great.

If Donald Trump got his way we would see a return to a Nixon-style government. During the Nixon administration the White House engaged in unprecedented politicization of the FBI, CIA, and Justice Department, strong-arming political opponents and drastically expanding the so called Imperial-Presidency. This was a stain on our history, a dark chapter in American politics, one that we need to be careful not to repeat.

To be fair to Mr. Trump his campaign has tried to clarify that he simply wants to "investigate" Mrs. Clinton to see if there is anything else that did not come up earlier, but those clarifications seem to have fallen on deaf ears. Many former Republican prosecutors have publicly denounced this shocking rhetoric. They have vigorously asserted that the Department of Justice is not a political tool, and to even suggest that it be used as such is dangerous and undemocratic.

This should be an issue that can unite Americans of all political affiliations. Republican or Democrat, liberal or conservative. We can all stand opposed to Presidential overreach, to the politicization of justice, and to the suggestion that political opponents should be jailed. In fact many of the most frightened commentators on this issue were conservatives, men and women who have been concerned about the increase of the Imperial Presidency during the past four or five Presidencies and who watched Donald Trump’s statement with shock and fear.

Make no mistake, threatening to prosecute and imprison your opponent is a threat to democracy, to freedom, and to the American way of life.