For now, Ms. Silver is sticking with Mr. Trump but she is part of a shrinking pool: Female voters’ support for the first-time candidate dropped 12 percentage points among likely GOP voters after last week’s CNN debate, according to a CNN/ORC poll conducted Sept. 17-19. The poll has a margin of error of plus or minus 3%.

That decline in support helped drive down Mr. Trump’s standing in the primary field. Although still the front-runner, his backing tumbled by eight percentage points, to 24% from 32% in a CNN/ORC poll conducted Sept. 4-8. Of those who tuned in to watch the debate, 31% of the likely GOP voters said he did the worst job—the highest percentage of any candidate…

“He’s kind of brutal toward women,” said Ms. Owens, who supports Ben Carson, a retired neurosurgeon and another political newcomer. She added that she questions whether women would be appointed to top positions in a Trump administration.

Mr. Trump’s female backers say they aren’t offended because his blunt rhetoric is just part of his tell-it-like-it-is style.