Democrats, looking at a new nine-point poll lead for Mrs. Clinton, began wondering whether winning might be easier than they thought. David Axelrod, who ran President Obama’s campaign, joked that Hillary Clinton should take the summer to tour the national parks and let Mr. Trump destroy himself. Mr. Trump’s meltdown, said Senator Kirsten Gillibrand of New York, is “a more permanent turning point.”

Any celebration by Mr. Trump’s opponents seems more than a bit premature. He is unlikely to go anywhere soon. Because what, really, has he suffered, besides a drop in the polls that might prove fleeting? In the month just ended, he very nearly matched the money raised by Hillary Clinton’s big-donor juggernaut, most of it in small contributions. His rallies drew thousands. This week a CNN reporter interviewed people at one Trump rally about Mr. Trump’s attacks on Khizr and Ghazala Khan, the parents of a soldier who was killed in Iraq. The vast majority of Mr. Trump’s fans were not only untroubled, but were willing to stand in line for hours to hear him say the same things all over again.

The idea that Mr. Trump will quit if his all-important poll numbers fall far enough seems like wishful thinking. A look at his business record suggests that as long as the money keeps coming in, Mr. Trump will fight, and if he loses, he’ll litigate. He is already talking about a rigged system, cherry-picking voter registration laws that don’t favor him as proof.

It is also highly unlikely that there will ever emerge a “better” Mr. Trump. We are far more likely to witness an even worse one. His support isn’t contingent on exhibiting “presidential” behavior, or shifting his energies to lofty discussions of public policy. In fact, it is contingent on the opposite. Lacking workable ideas or intellectual ballast, Mr. Trump’s candidacy thrives on his refusal to be “politically correct,” a term he deploys to give license to declarations that should be called bigotry, or cruelty, or verbal battery. That behavior is what many of his supporters most admire. He is speaking to people who disbelieve conventional politicians, who detest a Washington they think has betrayed them. He promises nothing of substance to ease their pain, but he gives voice to their rage.

So where does this leave Mrs. Clinton? It does not give her the luxury of sitting back and hoping Mr. Trump will implode, but it does present opportunities — to lure wavering Republicans and independents, not merely by stoking outrage at his statements, but by addressing in policy terms the economic anxiety and fear that underlie Mr. Trump’s appeal, as well as lingering distrust of her. Instead, she played into that distrust this week by repeatedly asserting untruthful claims about her careless handling of government emails.