Here, in this 14-minute interview, I explain why Mary Barra, the tough, embattled CEO of General Motors (GM) displaced IBM (IBM) chief Ginni Rometty as the top-ranked woman on Fortune’s 2015 MPW list. Rose and I also talked about one investor who has put big money behind both these chief executives: Berkshire Hathaway’s (BRKA) Warren Buffett. (All three—Buffett, Barra, and Rometty—will be at the Fortune Most Powerful Women Summit, which Fortune.com will live-stream October 13 and 14 from Washington, D.C.)

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Rose asked me about Ruth Porat, the former Morgan Stanley (MS) chief financial officer who moved to Google (GOOG) in May, and is now CFO of both Google and its new parent, Alphabet—a dramatic career change that I got the exclusive inside story on and explain in “The Google Effect” in Fortune‘s current MPW issue. Another exclusive story in the current issue, by Fortune‘s Jennifer Reingold, describes Angela Ahrendts’ transformation from Burberry (BURBY) CEO to head of retail at Apple (AAPL). “It was an inspired choice, but not an obvious choice,” said Rose about Apple CEO Tim Cook’s decision to hire Ahrendts. As I told Rose, Cook didn’t need a techie to refashion Apple’s stores; he was looking for “a leader and a culture carrier,” I said.

Rose and I couldn’t resist talking about Carly Fiorina, who is the first alum of the Fortune MPW list ever to run for the White House. I recalled interviewing Fiorina 17 years ago at Lucent Technologies (ALU), when she was a little known, rising-star executive at the telecom giant. And I saw early signs of her political savvy way back then.

That year, 1998, Fortune put Fiorina on the cover of its first MPW issue. The next summer, she was recruited to be CEO of Hewlett-Packard (HPQ). Fiorina led HP for six years, until the board fired her in 2005. Now she is the sole female GOP Presidential candidate, and tonight, she faces a make-or-break moment on the main stage of the Republican debate.