Kendal Unruh is on a mission — a God-given mission, she says — to stop Donald Trump becoming the next US president.

She does not want to leave things to fate, nor to Hillary Clinton — she wants to take him down, from inside his own party.

Ms Unruh is a Republican from Colorado, and she is the grassroots leader of the #NeverTrump movement.

"Donald Trump is not a Republican, bottom line," she says.

"He's a populist and he's a protectionist and all of his policies reflect that.

"I've spent my entire adult life for 30 years trying to reflect the platform as a conservative, values-based platform."

Kendal Unruh says everything about the Trump campaign smacks of cult-like behaviour. ( ABC News )

'We have no party left if he's our nominee'

It is this schism that is at the centre of the Republican Party's problem right now. Is Mr Trump genuinely a Republican? Is he even a conservative?

Ms Unruh said Mr Trump has stolen the Republican Party.

"That's exactly what this is about. We're truly about saving our party," she said.

"We have no party left if he's our nominee, because he has then changed what the brand means to be a conservative."

Ms Unruh grew up in a cult, a Christian following called The Move. At the age of 20 she left, then found and joined the Republican Party.

Mr Trump, she said, "absolutely" reminds her of a cult leader.

"You wouldn't have even had to have grown up in a cult to recognise cult-leader tendencies — if you look at this undying devotion in the followers — because that's what the problem is here," she said.

Ms Unruh said everything about the Trump campaign smacks of cult-like behaviour.

"Anything that came out, no matter how repulsive it was, no matter how wrong it is, no matter how it was proven that his policies are not going to make America great again … none of it mattered," she said.

"The fear and the anger had been demagogued in such a way that their faces were set like flint and it's like they have blinders on."

Trump 'might be a force for creative destruction'

As the Trump campaign appears to spin out of control, with as much "friendly fire" coming from within Republican ranks as there is from across the aisle in the Democratic Party, can Mr Trump really win the presidency?

Will he even make it to election day?

Some, like political historian Geoffrey Kabaservice, doubt his longevity and are already turning their minds to asking: What next?

"I think we're going to have to figure out what the Republican Party is going to be after Donald Trump," he said.

"He's clearly a force for destruction but he might be a force for creative destruction.

"I think he's also shown that a lot of people at the base don't actually care as much as we'd thought previously about the Republican nominee toeing a very hard line on these certain ideological points."

Geoffrey Kabaservice said the Trump campaign has identified core issues with broad appeal. ( ABC News )

Mr Kabaservice believes Mr Trump has done the GOP a service by identifying core issues with potential appeal to a broad base, "particularly the white working class about being hard-done-by in terms of the last economic disaster".

"In terms of being very worried about jobs, being very worried about immigration, being very worried about trade … they hadn't felt listened to by any nominee of either party up until Trump came along," he said.

The Godfather, ever the useful political reference point, is relevant here too, Mr Kabaservice said.

"Every once in a while the Mafia families have to battle it out with each other to get rid of the bad blood," he said.

"Maybe Trump was the catalyst for that kind of argument and discussion.

"Maybe in that sense they'll thank him later on."

Watch Foreign Correspondent at 9.30pm on ABC TV.