Donald Trump has claimed that by November he will have won over any Republicans who have lingering doubts about him.

But a new poll suggests that almost one in five registered Republicans want him to drop out of the race, even at this late stage.

The publication on Wednesday of the survey conducted by Reuters/Ipsos, underscores the disunity within the Republican Party and the deep reservations many have about the man they have nominated as their candidate.

Mr Trump was speaking in North Carolina (AP)

Earlier this week, it was announced that a conservative activist and former CIA operative, Evan McMullin, was running as an independent to try and stop Mr Trump securing the White House. Mr McMullin, 40, who formerly worked for Goldman Sachs, said there was a need for an alternative option for conservatives to the New York tycoon.

“In a year where Americans have lost faith in the candidates of both major parties, it’s time for a generation of new leadership to step up,” he told reporters.

Also, this week, a group of 50 Republican national security officials published an open letter in which they said Mr Trump was not suitable to be the nation’s commander-in-chief.

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“From a foreign policy perspective, Donald Trump is not qualified to be president and commander-in-chief,” said the letter. “Indeed, we are convinced he would be a dangerous president.”

Mr Trump is currently at the centre of new controversy following comments in which he appeared to suggest the only way to stop Ms Clinton appointing liberal judges if she becomes president, would be to shoot her.

“Hillary wants to abolish, essentially abolish the Second Amendment,” he said, referring to the piece of legislation that gun rights activists claim gives them the right to bear weapons.

“If she gets to pick her judges, nothing you can do, folks. Although the second amendment people, maybe there is.”

Amid a storm of outcry, Mr Trump insisted he was merely talking about rallying gun rights supporters to his side ahead of the election. The Secret Service said on Twitter it was aware of the comment.

The comment was just the latest of a series of incidents in recent weeks that have left many Republicans struggling to find a way to support him. Last month, he seemed to invite Russia to hack Ms Clinton’s emails - something he later said was merely a joke - and then he became involved in a bitter fight with the parents of a dead American soldier who had spoken against him at the Democratic National Committee.

The findings of the Reuters poll suggest 19 per cent think the New York real estate magnate should drop out, 70 per cent think he should stay in and 10 per cent say they “don't know”. The poll was conducted between August 5-8. The poll has a confidence interval of six percentage points.

Among all registered voters, some 44 per cent want Mr Trump to drop out. That is based on a survey of 1,162 registered voters, with a confidence interval of 3 percentage points. That is nine points higher than his support for the presidency in the latest Reuters/Ipsos tracking poll registered on Monday.