It has helped to fund an array of new nonprofit groups dedicated to taking on Mr. Trump. Its ranks include some of the left’s most prolific donors, such as the billionaire investors George Soros and Tom Steyer. This past week’s meeting drew appearances from several Democratic politicians, including Representatives Adam B. Schiff of California and Pramila Jayapal of Washington, as well as Senator Jeff Merkley of Oregon and Governor-elect Jared Polis of Colorado, a former Democracy Alliance donor.

The House Democratic leader, Representative Nancy Pelosi of California, a favorite of the donor class whose bid to be elected House speaker has been complicated by opposition from her party’s left flank, appeared with a handful of newly elected female Democratic members of Congress at a reception on Friday night celebrating female leaders. She was introduced as “the original badass woman in Washington and the next speaker of the House” by Lee Saunders, president of the American Federation of State, County and Municipal Employees, according to an attendee.

At the conference, which was closed to journalists, hundreds of donors and operatives kibitzed and debated the lessons of the midterms and the party’s options for 2020 in formal sessions and sideline gaggles. A New York Times reporter was escorted by an alliance staff member away from a second-floor banquet hall that hosted catered meals and a Thursday evening reception with an open bar and passed hors d’oeuvres, including tuna poke in waffle cones, and prosciutto and mozzarella skewers with a balsamic glaze.

In interviews on the sidelines of the conference, most donors seemed bullish on the emerging strategy, which amounts to a shift of sorts. In the weeks after Mr. Trump’s election, some in the group had warned of dire consequences if the party did not win back the white suburban and Rust Belt voters who had voted Democratic in recent presidential elections before swinging to Mr. Trump.

“The data bears out that there is in fact a new American majority of people of color and progressive white voters,” said Steve Phillips, a Democracy Alliance donor who participated in a Thursday panel about winning elections in the age of Trump. Mr. Phillips, who was solicited afterward by a succession of activists seeking support for groups targeting minority voters, said in an interview that “a lot of the donors are stepping up” to support such groups.

Mr. Phillips has long called for Democrats to forsake centrist appeals and candidates, including in the 2020 presidential primary, and he suggested that other donors would be wise to do the same. “We should certainly reduce the amount of resources we put in that direction if we want to win,” he said.