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.

Over the past week, Trump went on a spree of gaffes and provocations, including picking a feud over sacrifice with the parents of a slain American soldier. That sequence led to an increasing number of Republicans publicly announcing they will not vote for Trump. Yet none of those comments involved jokes about political murder.

As is often the case, the things that Trump says are out of the mainstream of political discourse, but not entirely novel. He has a knack for taking comments from the fringe and turning them into talking points for his campaign. Take for example his suggestion—ripped from the headlines of the National Enquirer—that Ted Cruz’s father was implicated in the Kennedy assassination. In 2010, Nevada Senate GOP candidate Sharron Angle talked about the potential need for “Second Amendment remedies” to tyranny. Angle was widely condemned, and went on to lose to Senator Harry Reid in the midst of a Republican year.

Clinton campaign manager Robby Mook quickly condemned Trump’s comment, saying in a statement, “This is simple—what Trump is saying is dangerous. A person seeking to be the President of the United States should not suggest violence in any way.”

The Trump campaign, meanwhile, claimed that Trump’s comment had nothing to do with the use of guns. “It’s called the power of unification—2nd Amendment people have amazing spirit and are tremendously unified, which gives them great political power,” spokesman Jason Miller said in a statement. “And this year, they will be voting in record numbers, and it won’t be for Hillary Clinton, it will be for Donald Trump.”

The Secret Service typically investigates even humorous suggestions of violence against presidents and presidential candidates. In 2012, washed-up rocker Ted Nugent said, “We need to ride into that battlefield and chop their heads off in November,” adding, “If Barack Obama becomes the next president in November, again, I will either be dead or in jail by this time next year.” Secret Service agents interviewed him about that comment, concluding he was not a serious threat. Trump’s comment is particularly unusual because he himself is under Secret Service protection. They won’t have to look hard to find him.