Mandela Barnes, the former lieutenant governor of Wisconsin, abandoned his campaign for the Democratic nomination for governor on Thursday.

His exit came as State Representative Francesca Hong, a democratic socialist, has built a broad base of support and polled well ahead of Mr. Barnes and other more moderate candidates. In a message posted online announcing his exit, Mr. Barnes said “it has become very clear who our nominee is going to be.”

Ms. Hong’s campaign has energized voters across the state in recent weeks, drawing a younger crowd to campaign events and pressing a platform that includes allowing local governments to raise income taxes on high earners and putting a freeze on the construction of new data centers.

Some Democrats, however, have expressed concern that Ms. Hong’s policies might be unpalatable to moderate voters in the general election. Wisconsin is about evenly divided by Republicans and Democrats. Gov. Tony Evers, the Democratic incumbent, decided not to seek a third term.

Representative Tom Tiffany is expected to be the Republican nominee.

The primary election is set for Aug. 11. Ms. Hong still faces several opponents in the primary, including David Crowley, the Milwaukee County executive, who is running with Mr. Evers’s endorsement.

Mr. Barnes served for four years as lieutenant governor under Mr. Evers. But rather than seek a second term as lieutenant governor in 2022, Mr. Barnes ran for the U.S. Senate and lost to Senator Ron Johnson, a Republican, even as Mr. Evers won a second term. That loss raised doubts among many Democrats about Mr. Barnes’s electability.

Though Mr. Barnes entered the race for governor with strong name recognition, he struggled to build momentum in a large and fractious primary field. As Ms. Hong consolidated support from the party’s left wing this summer, establishment-oriented Democrats looked for a relatively moderate candidate but struggled to coalesce.

Lt. Gov. Sara Rodriguez seemed to be emerging as the establishment’s preferred candidate this month, but her bid unraveled when problems with her campaign finance reports emerged. After she withdrew from the race, Mr. Crowley, who had previously suspended his campaign amid woeful poll numbers, announced that he was getting back in. Mr. Evers bypassed Mr. Barnes, his former governing partner, and endorsed Mr. Crowley.

But Ms. Hong has remained in command of the race. A Marquette Law School poll released this week showed Ms. Hong with 46 percent of the vote, 25 points ahead of Mr. Barnes, her nearest rival. Mr. Crowley was in a distant third place.

Ruth Igielnik contributed reporting.

This is a developing story. Check back for updates.