In June, 44% of white women had a favorable view of Mrs. Clinton, compared to 43% who didn’t. In July, those numbers moved in the wrong direction for Mrs. Clinton: Only 34% of white women saw her in a positive light, compared to 53% who had a negative impression of her, the poll found.

Mr. Obama fared poorly with white women voters in the 2012 election, losing them to Republican challenger Mitt Romney by 14 points.

For Team Clinton, the latest poll numbers are a worrisome development. Mrs. Clinton is unlikely to match the African-American turnout that propelled Mr. Obama to two presidential victories, so she has to make up the difference somewhere else. Women eager to see a woman in the White House is a logical group to target…

Among white women with at least a college degree, 51% had a positive view of Mrs. Clinton and 38% a negative as of June. In July, those numbers had turned to 43% positive and 47% negative.