On Lisa Hoberg’s phone, the group chat with what she calls her “mom friends” is a politics-free zone. In the political hotbed of suburban Phoenix, it seemed safer that way. Why risk ruining 15 years of friendship by bringing up Donald J. Trump?

That meant that some of Ms. Hoberg’s closest friends had no idea she, a lifelong active Republican, had gone through a major political transformation — one that surprised even her sometimes. It meant her friend, Jill Aguirre, a 59-year-old mortgage officer, had never mentioned her worries that immigration was leading to crime at her daughter’s college campus. And she had no idea how strongly Debbie Samartzis, a 57-year-old interior designer who was a registered independent for much of her life, felt about abortion rights.

But it’s hard to hold back in an election year.

When Ms. Hoberg, 50, asked her mom friends to discard the informal politics ban and sit down to talk, they readily agreed to fill up their wine glasses around her table and let a reporter listen in.

Their conversation could have consequences. These are women poised to play a critically important role in this year’s election, a contest that may be remembered for its historic gender gap. They are the sort of women — college educated, suburban, moderate — that Vice President Kamala Harris is counting on in overwhelming margins, hoping their turnout will swamp that of working-class men who favor Mr. Trump.

They are voters Mr. Trump has, in fits and starts, tried to win over. And they explained clearly why his overtures weren’t working.

With a bit of chagrin, Ms. Hoberg says she voted for Mr. Trump eight years ago because he “had not offended me a fraction of the time that I am offended by him now.”