Donald Trump’s campaign entered full-on banana republic territory when he threatened to prosecute his political rival, Hillary Clinton, if he is elected president.

“If I win, I am going to instruct my attorney general to have a special prosecutor to look into your situation,” Trump said. “There’s never been so many lies, so much deception. We’re going to have a special prosecutor.”

The threat came after a Trump rant about Clinton’s e-mail server, but he didn’t leave it there. Later on, he interrupted to say that if he was president, she’d be in jail. And, inevitably, on twitter:

Clinton has been criticized for doing government business on a private e-mail server she kept in her home. But an exhaustive FBI investigation found no evidence that classified information was lost, only that Clinton was careless in her arrangements.

Despite that conclusion, and unprecedented transparency into the details of FBI interviews, Trump and his campaign surrogates have insisted that the investigation was rigged.

But in going so far as to promise the politically motivated prosecution of a defeated political rival, Trump set a new a low for pushing modern constitutional norms in the United States. Few could recall any recent precedent for such a threat. Eric Holder, the former Obama administration Attorney General, said Trump’s bluster underscored his lack of qualifications.

These fears resonate doubly around a nominee whose statements on the freedom of press, freedom of religion, and the independence of the judiciary have already led constitutional scholars to fret, in the words of one, that “this is how authoritarianism starts, with a president who does not respect the judiciary.”