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Donald Trump just promised to abuse his power as president and prosecute Hillary Clinton if elected.

“Lock her up!” has been the unofficial motto of the Trump campaign since the Republican National Convention in July. But though he clearly enjoys it, Trump has never said that himself. That changed on Sunday night. During a discussion of Clinton’s use of a private email server, Trump dived into uncharted territory in the history of presidential politics. He promised that, if elected, he would prosecute Clinton for her use of the server—that, in other words, he would use the power of the presidency to punish a political opponent. And then this happened:

This is madness. Thirty minutes in, saying this debate is off the rails doesn’t even cut it. It started with Trump becoming the snorting embodiment of an alt-right message board by turning sexual assault allegations into a carnival. And then Trump promised that, at the start of his presidency, he would actively hound his enemies. The rest of this debate could be the most substantive hour in the history of presidential politics, but it wouldn’t change what Trump just said, which is that he would rule the country as an authoritarian who would use the presidency not just as a sounding board for people who are deservingly on the fringes of American political life, but to actively subvert democracy.