The transition of power begun in the United States with two words trending on social media that evoked the worst nightmares of those who had fought to repel the campaign of now President-elect Donald Trump believing him to be a hate-monger and an inciter of violence. “Kill Obama”.

This is what one supporter in the crowd listening to Mr Trump making his victory speech at the Midtown Hilton Hotel in Manhattan in the early hours of Wednesday seemingly - and not everyone heard it the same way - yelled out as Mr Trump was in the midst of a victory speech that pundits mostly greeted as magnanimous.

“She fought very hard,” the victor said with regard to Ms Clinton’s suddenly vanquished campaign, adding that the country owed the former Senator and first lady a “major debt of gratitude” for her service through her career. And indeed most in the hotel clapped in approval.

But it was while Mr Trump was in mid-flow, specifically reiterating his promise to launch an intense programme to rebuild America’s failing infrastructure, when the voice is heard ringing out from somewhere deep in the throng before him. Video clips of the moment capture his young son, Barron Trump, apparently flinching in disbelief at what he had just heard. Or fear.

While the name ‘Obama’ can clearly be heard coming from the man who is off camera, the rest is a little more open to argument. Most listening indeed hear him utter the word ‘kill’, others, notably defenders of Mr Trump taking to Twitter, insisted he said ‘repeal’.

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Repeal is possible, though of course after the transition period between now 20 January 2017 Mr Obama will be preparing to leave office anyway. And you repeal laws. You impeach presidents.

If “kill” was the word - and it would explain the startled look on the younger Trump - it came just from one man. But from a man attending a rally of a president-elect who throughout his campaign faced allegations that he was deliberately dropping a coded message to supporters sanctioning violence. And with it the heckler seemingly also touched on the other dark seam of the 2016 race, a still simmering racist backlash among some white voters against a sitting president who is black.

Mr Trump apparently did not hear it as he was making his way through the address almost no pollster in America ever imagined he would be making. Within an instant of the alleged profanity he had moved on to pledging greater support for US veterans.

Not once, but twice during the campaign, Mr Trump delivered comments that to many sounded like calls to his supporters, and especially defenders of gun-owning rights, to consider killing themselves, with Ms Clinton as the intended victim, not the sitting president.

In September in Miami he mused at a rally what would happen if Ms Clinton’s body guards were forced to drop their guns, a reference to his claim that she wanted to take everyone else’s guns away. Ms Clinton “wants to destroy your Second Amendment” right to bear arms and called on her security detail to disarm, so we “can see what happens,” he said.

Earlier in the summer at a different event, Mr Trump similarly seemed to invite violence against the former first lady when he warned a crowd of supporters that unless “the Second Amendment people” stopped her she would chose anti-guns justices to sit on the US Supreme Court.

“Hillary wants to abolish, essentially abolish the Second Amendment,” Trump said to boos from the crowd. “By the way, if she gets to pick her judges, nothing you can do folks,” he then added.