Once more embroiled in controversy, Donald Trump has been accused of inciting violence against Hillary Clinton for a second time under the guise of speaking up for gun owners’ rights.

The Republican nominee is meanwhile striking back at Robert Gates, who served as Defence Secretary under both George W. Bush and Barack Obama, for dismissing him as “beyond repair” when it comes to national security.

In a withering article in Saturday’s Wall Street Journal, Mr Gates said that the Republican presidential nominee is “stubbornly uninformed about the world and how to lead our country and government, and temperamentally unsuited to lead our men and women in uniform.” He concluded: “He is unqualified and unfit to be commander-in-chief.”

Still reverberating through the campaign are remarks made by Mr Trump in Miami on Friday evening, when he told supporters that 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”.

“I think what we should do is she goes around with armed bodyguards, like you have never seen before. I think that her bodyguards should disarm, right? Right? Think they should disarm. Immediately, what do you think? Yes? Yes. Yeah. Take their guns away. She doesn’t want guns. Let’s see what happens to her.”

Mr Trump had just completed a few days of relative discipline - he resisted the temptation, for instance, to denigrate Ms Clinton for taking days off the trail to recover from pneumonia - that many observers had put down to the influence of his new campaign chief, Kellyanne Conway.

But he seems suddenly now to be reverting to form, testing again whether his talent for creating controversy and stirring outrage rather than sticking to the script set by his advisers might still be the more effective way to scoring ultimate victory at the ballot box.

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Before flying to Miami on Friday, Mr Trump used an event at his brand new hotel in Washington DC, just blocks from the White House, to abruptly back away from his ‘birther’ past when he questioned whether President Obama had been born in the United States while saying in the same breath that it was Ms Clinton who had raised the whole issue first and not him.

Both that claim, for which there is no evidence, and his remarks about Ms Clinton losing her secret service protection have, inevitably, served to stir a new storm of Democratic indignation.

“Where the conspiracy theories started were like the darkest corners of the Internet, which is where Donald Trump thrives,” Hari Sevugan, an Obama spokesman in the 2008 primaries, told Politico with regard to who started the birther absurdities. “They became the founders of the tea party and are now fueling Donald Trump.”

Leading the condemnation of his Miami remarks was the Clinton campaign itself. At an event earlier this summer, 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.

That comment was deemed so egregious that his campaign was later interviewed about it by the Secret Service.

Mr Trump has “a pattern of inciting people to violence,” the Clinton campaign spokesperson, Robbie Mook, said later on Friday.

“Whether this is done to provoke protesters at a rally or casually or even as a joke, it is an unacceptable quality in anyone seeking the job of Commander in Chief,” he wrote in a statement. “This kind of talk should be out of bounds for a presidential candidate, just like it should be out of bounds for a presidential candidate to peddle a conspiracy theory about the President of the United States for five years.”

Her press secretary Brian Fallon later speculated on social media that either Ms Conway had “suddenly determined jokes about assassination would help boost Trump with independents... or the dog is off his leash”.