Billionaire Tom Steyer dropped out of the presidential race after he finished behind Joe Biden in South Carolina on Saturday. "Honestly, I can't see a path where I can win the presidency," Steyer told supporters during an election night party in Columbia, South Carolina, adding he would continue to support grassroots causes.

"This has been a great experience. I have zero regrets," Steyer said.

After Steyer spoke, some staffers appeared stunned, others frustrated. Organizer Nicola Hemphill wiped streams of tears from her face as she clung to friends. "South Carolina was a slave state," Hemphill told CBS News. "This is the first candidate I have ever seen put black people first. And he did it on the national platform."

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Hemphill described what she believes will become Steyer's legacy: "Tenacity. Entrepreneurship. He cares about our lives."

Steyer invested heavily in the Palmetto State, building a campaign infrastructure and spending more than $17 million on ads there. He had the most staff in South Carolina, with 102 staffers, and spent 23 days campaigning in the state.

Before the primary, Steyer's efforts appeared to pay off, as polling in the run-up to the primary put him in third behind Biden and Sanders. But he failed to earn any delegates in the other three early-voting states, Iowa, New Hampshire and Nevada. CBS New projects that Biden will win the South Carolina primary and exit interviews indicated he had a big lead.

According to results of CBS News exit polling, Steyer voters in South Carolina have a significantly stronger affinity for Biden than for Sanders. Among Steyer voters, 71% have a favorable opinion of Biden, but only 43% have a favorable impression of Sanders.

The billionaire philanthropist was among the first to call for President Trump's impeachment and has been one of the most vocal to sound the alarm about climate change.

Steyer vowed to support the Democratic presidential nominee, saying any Democrat is "a million times better than" Mr. Trump. He also criticized Republican South Carolina Senator Lindsey Graham, calling him a "disaster for the people here."

Seated in the first row for Steyer's announcement, supporter Courtney Young from Columbia, South Carolina, said she will "absolutely" consider Steyer's endorsement moving forward if he chooses to back another presidential contender. "It's a sad night, but we have so much respect for Tom," she said.

Young said she appreciated Steyer's prompt announcement following his projected third place finish. "He knew when to hold them and when to fold them in this space. And he was true to his word."

"When the Lord closes a door he opens a window," Steyer said Saturday night. "I will find that window and crawl through it with you, I promise you that."

Grace Segers, LaCrai Mitchell and Nicole Sganga contributed to this report.