The Business Relationshiptown hall debate between Hillary Clinton and Donald Trump turned ugly very quick, with each candidate hurling attacks based mostly on previous issues that had been a part of a campaign that seems like it has been going on for forever.

But Trump launched something very new on Sunday, something that many people feel crossed a line.

During one particularly contentious exchange, Trump pledged that if he won the presidency, he would appoint a special prosecutor to investigate Clinton's use of a private email system during her time as the secretary of state.

"You'd be in jail," Trump said to Clinton.

The moment came and went relatively quickly, with numerous other moments gaining plenty of attention.

The pledge, however, stuck with many as a particularly terrifying statement.

Former attorney general Eric Holder weighed in, noting that Richard Nixon attempted a similar maneuver -- an action that resulted in the resignation of his attorney general.

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Trump's campaign felt the moment was strong enough to tweet out.

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Plenty of other politics watchers also noticed the moment.

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BONUS VIDEO: Watch Trump lurking behind Clinton during the debate.