Donald Trump’s three days of relative calm ended dramatically on Tuesday, as he appeared to crack a joke about assassinating Hillary Clinton during a rally in Wilmington, North Carolina. Trump has argued that even conservatives who don’t like him should vote for him in order to prevent the Democrat from making Supreme Court appointments. It was in that context that Trump made the remark.

“Hillary wants to abolish, essentially, the Second Amendment,” he said. “By the way, and if she gets the pick—if she gets the pick of her judges, nothing you can do, folks. Although the Second Amendment people, maybe there is, I dunno.”

The suggestion that the assassination of a presidential candidate—or the killing of Supreme Court justices, or an armed insurrection, depending on interpretation—could solve a policy dispute is a shocking new low for a campaign that has continually reset expectations. Trump’s defenders often scold the media for being humorless, or taking Trump’s comments too seriously. So let’s preemptively dismiss that counterargument: This aside was clearly intended to be a joke. It is also entirely shocking and appalling, even in that context.

At no point in recent American history has the nominee of one of the two major parties even jested about the murder of a rival. (Watch the man in the red shirt and white beard behind Trump to see his reaction in the clip above.) The recent prevalence of “lock her up!” chants at Trump events look, from some angles, like a disturbing echo of politics in less stable nations, where vanquished political rivals are imprisoned or worse. Trump’s comment today blows well past that line. Even unserious suggestions of killing can be a dangerous thing, as St. Thomas Becket might attest.