Donald Trump has a well-documented problem with women.  Several surveys show that about 70 percent of women rate Trump unfavorably.  And recent polls by CBS and CNN both suggest that he could lose female voters to Democrat Hillary Clinton by at least 25 percentage points in November.

Even worse for the presumptive Republican presidential nominee, his image among women has grown increasingly negative over the course of the primary campaign — a campaign in which Trump’s offensive comments about women became a major issue.   Indeed, a majority of women now rate Trump very unfavorably.

In fact, the percentage of women who rated Trump very unfavorably in YouGov’s biweekly surveys has increased significantly — from around 45 percent in January to nearly 60 percent by the end of April.  Meanwhile, the percentage of men who rated Trump very unfavorably hasn’t really changed.

This pattern is especially pronounced among political independents.  The graph below shows a 20-point increase in the percentage of female independents rating Trump very unfavorably.  Again, Trump’s image among independent men is more stable, making the gender gap increasingly pronounced.

The same pattern also emerges in RAND’s Presidential Election Panel Survey (PEPS) — a project that re-interviewed more than 2,600 people in March who were also surveyed in December.   Among female independents, the percentage who rated Trump very unfavorably increased from 50 percent in December to 56 percent in March. Male independents did not shift their views of Trump. In fact, after accounting for several other factors, gender was the only factor significantly associated with those who rated Trump more unfavorably in March than in December.

The results from both surveys are consistent with Lynn Vavreck’s findings about the campaign ads criticizing Trump for his statements about women. She found that women who were randomly assigned to view an ad by Our Principles PAC, in which Trump’s insulting quotes about women were read aloud by women, rated Trump 19 points more unfavorably relative to those who had not seen the ad.  “Among men,” Vavreck writes, “this shift was 1 point.”

These results are also consistent with a long line of political science research showing that campaign appeals to deeply held social identities like race, religion and gender can cause people to change their opinions about politicians.  It is not too surprising, then, that the current presidential campaign, in which both Republicans and Democrats have criticized Trump for sexist statements, has increasingly turned women against his candidacy.

To be sure, it is still about six months before Election Day.  But with Clinton and the Democrats figuring to make Trump’s past comments about women an even bigger campaign issue than did his Republican rivals, Trump’s campaign may struggle to appeal to women voters in general, and female independents in particular — both of whom could be crucial if he wants to close his sizable polling deficit against Clinton.

Michael Tesler is assistant professor of political science at UC Irvine and author of “Post-Racial or Most-Racial? Race and Politics in the Obama Era.