The New York Times detailed how Donald Trump’s advisers had pleaded with him to become a more disciplined, credible candidate. “Mr. Trump bowed to his team’s entreaties,” the Times reported. “It was time, he agreed, to get on track.”

Trump immediately denounced the story. He hadn’t “bowed” to anyone. He wasn’t going to change. “I am who I am,” he tweeted.

That reaction reveals a key reason why Hillary Clinton, a deeply unpopular candidate, is running so far ahead. Trump firmly believes in his own wisdom and boasts constantly about defeating 16 opponents in the Republican primaries. And yes, he defied the predictions of virtually every political analyst, including us.

But the primary period is profoundly different from a general election. Trump might still be the same – “I am who I am” – but he’s now operating in a new world. A new universe, really. And he can’t, or won’t, understand that tectonic shift.

Once candidates get the nomination, once they actually have a chance of becoming president, the spotlight gets much brighter and hotter. Every word, every gesture, every innuendo becomes magnified, scrutinized, dissected.

Trump blames the media for his plunge in the polls, and in a way he’s right, because they’re taking him much more seriously. They are subjecting his words to a much sterner test, and holding him accountable for them. As a result, the outrageousness that earned him almost $2 billion of free TV time in the primaries is now being turned against him.

For months, he insulted just about everybody – Mexicans and Muslims, women and the disabled – while primary voters cheered him on. But once he became the nominee, and demeaned the parents of a slain Muslim soldier, or casually incited “Second Amendment people” to violence, the intensity of press coverage became his enemy, not his friend.

We are reminded of a story told by the late Charlie Mohr, a New York Times reporter covering Barry Goldwater in 1964. He was outside a campaign rally when a tearful woman burst out of the room and cried, “Stop them, stop those reporters, they’re writing down every word he’s saying.”

And it’s not just the media. In the primaries, Trump’s rivals were generally reluctant to attack him directly because they didn’t want to alienate his supporters. Now, Team Clinton and the Democrats are savaging him daily, joined by a steady stream of Republicans who have decided that, alas, Trump is who he is: undisciplined, unqualified and downright dangerous.

Sen. Susan Collins of Maine spoke for many of those Republicans when she told CBS why she couldn’t support her party’s nominee: “I always expected that he would evolve and change and that we would see a new Donald Trump after the primary. Instead, the constant barrage of the ill-informed and cruel comments continued.”

Another difference is the political landscape. Republican primary voters are much whiter, and more conservative, than the country as whole. Now Trump faces a national electorate that is only 70 percent white. And in many swing states, the voting population is even more diverse: about 50 percent white in Georgia, Nevada and Arizona, 40 percent in New Mexico.

Sure, he continues to attract large and enthusiastic crowds, but he willfully deludes himself into thinking those crowds reflect the wider voting population. For instance, he defended his attacks on President Obama as the “founder” of ISIS by telling radio host Hugh Hewitt, “Everyone’s liking it.”

Of course “everyone” who comes to a Trump rally was thrilled. But they won’t decide the election. To others, the comment was an outright lie, one more example of why he’s totally unfit to be president.

Voters are taking Trump more seriously, as well. As the election gets closer, they are viewing him through a different lens and holding him to a much higher standard. He’s no longer just a celebrity, a reality TV star who “tells it like it is.” Folks are starting to evaluate him as a possible president, and for some – particularly well-educated Republican women – that process is causing them to change their minds.

“I liked that he was politically incorrect,” Trish Grove, a banker in suburban Philadelphia, told The New York Times. “But now I feel, ‘enough already.’ He is not going to win a majority of voters by sounding offensive and ridiculous.”

No, he’s not. There is no New Trump, and no campaign shake-up will change that. He is who he is. And at last the country is starting to say, “Enough already.”

Steve and Cokie Roberts can be contacted by email at stevecokie@gmail.com.