Sarah Kendzior is a St. Louis-based commentator who writes about politics, the economy and media.

Several days ago, a video circulated comparing the reactions of Hillary Clinton and Donald Trump to potential threats on the campaign trail. Alerted to danger, Mr. Trump flails desperately, hiding himself in an enclosure of guards. Meanwhile, Ms. Clinton stares stoically as her own guards surround her, smiling and saying to the crowd, "Okay, here we are!"

The video was meant to highlight Ms. Clinton's cool-headed demeanour versus Mr. Trump's instinctive cowardice. Now, however, the video has a darker undertone: It is Donald Trump and his fans whom Ms. Clinton should fear, after Mr. Trump seemed to casually call for his opponent's assassination Tuesday.

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In his words: A look at some of Trump's most incendiary comments

"By the way, and if she gets the pick – if she gets the pick of her judges, nothing you can do, folks," he said at a rally, discussing the ability of the president to appoint members of the U.S. Supreme Court. "Although the Second Amendment people, maybe there is, I don't know."

"The Second Amendment people" refers to America's gun fanatics, many of whom have appeared at Trump rallies screaming "lock her up," "burn the witch" and other chants. The rhetoric at Trump rallies is so vicious and misogynistic that one featured a 10-year-old boy yelling "take that bitch down" as his mother stood by approvingly. (This incident would have dominated coverage had Mr. Trump not feuded with a baby at the same rally.)

Was Mr. Trump, as he now says, merely calling on the electoral power of this group? No. Was his hint for an assassination a joke? No. Moreover, does it matter? How do you joke about the assassination of your rival – or of any politician?

His comments are unprecedented in U.S. history – a history littered with political corpses. Mr. Trump was 17 in 1963 when John F. Kennedy was assassinated, 22 in 1968 when JFK's brother Robert and Dr. Martin Luther King were assassinated, and 34 in 1981 when then-president Ronald Reagan was shot. These were the formative political events of Mr. Trump's baby boomer generation. They were moments of collective national agony. They are never recounted in jest.

Mr. Trump's comments are so beyond the pale that they have prompted, yet again, speculation that he is trying to get himself thrown out of the race. This is too charitable an interpretation. His comments are in line with a campaign that has always been a test of his fans' limits and loyalty, of how much tolerance Americans have for bigotry and threats, and how much power Mr. Trump can wield over his base.

If someone assassinates Hillary Clinton, Donald Trump will abdicate all responsibility – but he will luxuriate in his own might. It is adoration he wants, and revenge he seeks as his beloved poll numbers fall. Though he runs as the candidate of "law and order," he has repeatedly called for chaos, at one point in 2014 proclaiming that "total hell," "disaster" and "riots" were necessary to make America great again. His loyalty is not to his country, but to how much influence he can hold, regardless who suffers – or who dies.

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Mr. Trump's disturbing comment comes less than two months after British politician Jo Cox was killed by a right-wing extremist during the lead-up to the Brexit referendum – a political climate resembling Mr. Trump's campaign. It arrives five years after Democratic congresswoman Gabrielle Giffords was shot in the head by a far-right extremist.

Prior to the attack on Ms. Giffords, Republican Sarah Palin had created a map with crosshairs showing Democratic targets – which included Ms. Giffords. After Ms. Palin tweeted the map, with "Don't retreat, instead – RELOAD!" – she dismissed it as a joke. In 2010, Ms. Giffords' opponent had campaigned against her under the slogan "Help remove Gabrielle Giffords from office, shoot a fully automatic M16 with Jesse Kelly." This was dismissed as a joke as well.

Since Ms. Giffords was shot in 2011, mass shootings and militia recruitment in the U.S. have both increased. Death threats toward women, spurred by social media, have risen as well.

But for Ms. Clinton, this climate of violence is nothing new. Speaking on health care in 1994, she was greeted by an armed mob, stoked by right-wing media, who screamed at her as she stood before them.

"She agreed for the first time to wear a bulletproof vest. Rarely had she felt endangered, but this was different," her biographer recalled.

Today, such incidents are no exception. Thanks to Mr. Trump, they are the rule.