The steely-eyed , stern-jawed author of the best-selling "Art of the Deal" is heading to Mexico City today, which means that by nightfall we ought to have Mexico's abject surrender.

After all, we've been promised that Donald Trump and his "best people" won't be pushed around by these other countries, not gonna happen, not any more.  Mexico has been "killing us, they're killing us at the border, they're killing us on trade," Trump says, because they're smart and we have weak, stupid negotiators -- "losers!!"

But when he's in charge, all that will change.

Sure, Mexican President Enrique Peña Nieto has called the idea of a wall absurd. Sure, he has likened Trump's rise to that of Hitler and Mussolini, who used economic discontent and bigotry as a means to power. But today, confronted by the orange magnificence of Trump in person, Peña Nieto will no doubt collapse like a birthday piñata, showering goodies all over the American people.  Tonight, when Trump speaks in Arizona, he'll no doubt be waving a signed promise by Peña Nieto to abandon NAFTA, stop the remittances of money across the border, build the 40-foot wall and of course pay for it as well.

Or maybe not.

The confident, snarling Trump of the Republican primaries, the man who insisted that "I will build a great, great wall on our southern border, and I will have Mexico pay for that wall," has suddenly turned weak, uncertain and vacillating. “There certainly can be a softening, because we’re not looking to hurt people,” he told a nodding Sean Hannity on Fox last week.

"So you have somebody that's been in the country for 20 years, has done a great job, has a job, everything else," Trump said. "OK. Do we take him and the family, her or him or whatever, and send them out? Are they gone? .... Do we tell these people to get out, number one, or do we work with them and let them stay in some cases?"

Two days later, Trump condemned the media for even suggesting that there might be a softening of his position.

“I don’t think it’s a softening,” he said. “I’ve had people say it’s a hardening, actually.”

As Trump has reminded us countless times, immigration has a high profile in this campaign because he alone put it there. This is the structure upon which he built his entire primary campaign, feeding his followers nonsensical promises about building an impenetrable wall that Mexico would be forced to finance, about deporting the 11 million illegal immigrants already here, taking their "anchor babies" with them.

“They’re gonna be gone so fast if I win, your head will spin.”

It was ugly, and when the venom that Trump spewed from the podium was reflected back to him by his crowds, he reveled in it, basked in it like a serpent sunning itself on a rock. These people who came here illegally were killers, rapists, drug dealers, he said, and those few who didn't fall into those categories were leaches drawn here to suck on the blood of American taxpayers.

But these days, facing a general election, that ugliness is less useful to him. Support among Hispanics has of course tanked, despite Trump's claims that "the Hispanics, they love me!" The number of people willing to support him in the black community has dropped so low that at this point, you could practically name them all individually.

But in Trump's calculus, that was to be expected. It was built into his strategy. What he did not expect, what has gotten him panicked, is that an overwhelming number of other Americans, including independents, women and college-educated white people, have heard his language, have recognized the bigotry and have rejected it. Younger voters in particular have found it repulsive, turning against Trump and the Republican Party that nominated him in unprecedented numbers.

Trump wasn't counting on that. He underestimated the basic decency of the American people, and the polls tell us that he's paying a heavy price for that mistake. So what we're witnessing now is a cynical attempt to back away from many of the ugly things that he has said and done over the past year, to project a more humane image. The problem is that once these things are seen, they cannot be unseen. We know who he is, because he has shown us.

Or as they say in Mexico, "Once thrown, a word and a stone cannot be returned."