Andrew Gillum and Stacey Abrams, progressive African-American Democratic candidates, may not have won their races for governor in Florida and Georgia (both are still too close to call). But the strategy they followed is still the best strategy for Democrats to win: inspiring, mobilizing and turning out voters of color and progressive whites.

I’ve argued for this strategy for years. In my 2016 book, I analyzed Barack Obama’s victories in the context of the country’s changing demographics. The implications of the Gillum and Abrams races are profound (to be clear, I did fund-raising for the efforts to elect both Ms. Abrams and Mr. Gillum, just as I did for Mr. Obama in 2008), and learning the right lessons from 2018 is key for Democrats as they look ahead to the 2020 elections.

Over the past 20 years, the best-performing Democratic candidates in statewide elections in Florida and Georgia have been Mr. Obama, Mr. Gillum and Ms. Abrams. (Hillary Clinton in 2016 was actually Florida’s highest Democratic vote-getter ever.) This year, Ms. Abrams dramatically increased Democratic turnout, garnering more votes — 1.9 million — than any other Democrat running for any office in the history of Georgia (and that includes Jimmy Carter, Mr. Obama and Mrs. Clinton).

Conventional wisdom dictated that both Mr. Gillum and Ms. Abrams did not give Democrats their best chance; more traditional, moderate white candidates were seen as the most competitive. In this view, moderate candidates can better appeal to and win over “swing” white voters.