South Carolina Democratic Party chairman Jaime Harrison emailed Democratic National Committee members Thursday to say he is dropping out and backing Perez.
Harrison was a distant contender -- far behind Perez and Minnesota Rep. Keith Ellison. "In a former job, I whipped votes for House Democrats. I know what a path to victory looks like," Harrison said in his email, acknowledging he couldn't win.
But with both Perez and Ellison within striking distance of the majority of the DNC's 447 voting members, Harrison's support could push Perez over the edge -- and make Harrison the kingmaker.
Vote-counting is nebulous, since some DNC members have not revealed their plans even privately, and there's no reason those who have committed to support one candidate couldn't change their minds at the last minute.
But a source close to Perez said Thursday that Harrison had about 30 supporters, and about 20 were expected to now back Perez. The source said Perez already had about 200 supporters -- but cautioned that Saturday's proceedings are hard to predict.
With several of the DNC's 447 membership slots vacant, 442 DNC members are eligible to vote Saturday. If all do so, it will take 222 votes to win.
Harrison's move comes days after New Hampshire Democratic Party chair Ray Buckley dropped out and endorsed Ellison.
A Perez spokeswoman said Harrison did not receive any commitment for a specific role within the party in exchange for his support.
"Every person who knows Jaime Harrison will say he is one of the smartest, most dedicated, and genuine leaders we know," Perez said in a statement. "Simply put, he's one of a kind. Jaime's commitment to the party is like no other and I'm proud to have his support as we both work together to invest in state parties, turnaround the DNC, and get back to winning."
Harrison's exit leaves South Bend, Indiana, Mayor Pete Buttigieg and Idaho Democratic Party executive director Sally Boynton Brown likely vying for third place, each with what Democrats tracking the race say are about 10 votes in their favor.
Buttigieg had hoped to emerge as the balloting went on Saturday in Atlanta. But the increasingly narrowing field before the election means the race could end too quickly for a third option to break out.