BOYNTON BEACH, Fla. — When Andrew Gillum, the Democratic candidate for governor of Florida, conceded the race a week ago, it did not seem like a tough call.

At the time, he was down by 84,000 votes to the Republican, Ron DeSantis, and hundreds of his disappointed supporters were standing in a pelting rain outside his headquarters in Tallahassee.

But Mr. DeSantis’s lead steadily dropped in the days after the election, narrowing to just 33,000 votes on Saturday. Florida’s secretary of state ordered a recount, and Mr. Gillum, heeding staff members who had urged him from the beginning to stay in the game, withdrew his concession. He did so reluctantly, according to staff members and associates, only after being bombarded by supporters and pressured by allies in organized labor who wanted him to go for a win — or at least go down with a fight.

“Basically, we all wanted him to come back,” said Afifa Khaliq, program director with the Service Employees International Union Florida chapter, which helped coordinate Mr. Gillum’s field operation. No one, she said, had planned for a situation in which the popular Tallahassee mayor lost the election. “This was not supposed to happen. We are all still shock.”