Among Republican strategists – the kind of political hacks who have actually worked on successful presidential campaigns – there has long been some serious head-scratching about the Democratic response to Donald Trump.

Why portray him as the scariest man alive? Why treat him as if his random brain farts will become reality?

“Democrats are taking Trump way too seriously,” one veteran GOP consultant told me at the Republican convention in Cleveland. “If you say he’ll destroy the world, that means you think he’s going to do what he says he’ll do. A more powerful attack is to say he’s fake. He can’t and won’t do any of it.”

This line of attack is a gutsy one because the payoff is less obvious. After all, it’s much easier to horrify moderate voters – and motivate the party base – with Trump’s plans to deport 11 million US residents, close the borders to a billion Muslims, launch a trade war with China and cozy up to Vladimir Putin.

In this target-rich environment, who has the time or energy to go after his credibility?

Why, Donald Trump does, of course.

This week the GOP nominee managed to flip-flop on his signature issue: the one that got him through all those noisy primary debates. The one that allowed him to destroy most of his rivals and connect at a visceral level with the party’s nativist core.

Of Trump’s top three opponents – Marco Rubio, Ted Cruz and Jeb Bush – two are Latino and one is married to a Latina. Trump tarred all three, despite their protestations, with the same brush of being soft on immigration.

And then, out of sheer desperation or stupidity, Trump decided this week to copy them. At a town hall-style show on Fox News, hosted by his unofficial adviser Sean Hannity, the GOP candidate rolled out his kinder, gentler immigration policy to a mixed response from the crowd.

“So you have somebody that’s been in the country for 20 years, has done a great job, has a job, everything else, OK. Do we take him and the family, her or him or whatever, and send them out? Are they gone?” Trump mused out loud.

“Or when somebody really has shown – you know, it’s called like the merit system – other than they did break the law in the first place, OK … So do we tell these people to get out, number one, or do we work with them and let them stay in some cases?”

And so it came to pass, with a rambling response on Fox News, that Trump demolished the foundation of his own campaign. Which naturally left his audience a little confused.

Trump may have previously given the impression that he thought all these undocumented immigrants were little more than a gang of murderers and rapists. But now, after some reflection, he concedes there may be some decent families mixed in with the gangs of thugs. Under Trump’s new plan, there would be no citizenship for these people, but there would be legal status after the payment of some back taxes.

This plan is otherwise known as the Obama proposal for comprehensive immigration reform.

“I’ve had very strong people come up to me, really great, great people come up to me,” he explained on Fox News. “And they’ve said, Mr Trump, I love you, but to take a person that’s been here for 15 or 20 years and throw them and the family out. It’s so tough, Mr Trump. I mean, I have it all the time! It’s a very, very hard thing,”

Then he turned to his crowd and asked, “Who wants those people thrown out?”

“I do!” responded one man.

This is a natural response from the people who have fueled the rise of Donald Trump, and their dismay at Trump’s total betrayal is only just emerging.

Mark Krikorian, the executive director of the nativist Center for Immigration Studies, told the Wall Street Journal the Trump campaign was over. “Whatever remaining chance he had to win the White House is gone,” said Krikorian. “The fact now that he has betrayed his base on the signature issue that he ran on seems to me the death knell of his candidacy as a practical matter.”

You may be forgiven for thinking that Trump wanted to deploy a “deportation force” to expel millions of undocumented immigrants. But when pressed about Trump’s paramilitaries on CNN, his new campaign manager Kellyanne Conway said meekly: “He has not said that for a while.”

Back in 2004, John Kerry’s campaign was destroyed for pointing out obtusely that he had voted both for and against funding the Iraq war. This flip-floppery led to TV ads of him windsurfing back and forth to the tune of the Blue Danube. As a result, it was hard to think of a less manly American leader in the midst of the war on terror.

If you’re wondering what Team Bush thinks of Donald Trump’s far more dramatic flip-flop, you don’t have to look that far. Jeb Bush, the low-energy brother who was so easily dispatched by Donald Trump in the GOP primaries, told WABC radio that the nominee’s reversals were “abhorrent”.

“Sounds like a typical politician,” Bush said. “All the things Donald Trump railed against, he seems to be morphing into. I don’t know what to believe about a guy who doesn’t believe in things.”

If only he had been capable of such quips in the primaries, he might now be working on his transition to government.

Of course, in later speeches and interviews, Trump suggested he might deport more people. Or fewer. Depending on the TV interview or crowd he’s talking to at the time.

Until now, honesty has been one of the very few areas where Trump has been running ahead of Hillary Clinton. While both candidates score poorly on such traits, Trump still maintained an edge, according to a recent NBC News/Survey Monkey poll. Even while losing badly overall to Clinton, Trump enjoyed a five-point advantage over Clinton on being honest and trustworthy. This is unlikely to last for much longer.

The bottom fell out of the Trump campaign last month after a disastrous convention season. He picked a miserable fight with a Muslim American gold star family, and gave a series of TV interviews that would have got him fired from his own show. Straight talk, no matter how offensive, was his last remaining quality.

People say that Trump learns nothing from his past errors, but that clearly isn’t true. A month and a couple of campaign managers later, Trump isn’t just repeating the same mistakes. He has learned how to make even bigger ones.