The board of the nation’s largest labor union, the National Education Association, voted on Saturday to support Hillary Clinton in the Democratic primary, concluding an endorsement process the NEA’s president described as “hotly discussed and debated,” leaving some members and state leaders divided between Clinton and her strongest challenger, Sen. Bernie Sanders.

At the request of the union’s president, Lily Eskelsen García, Clinton appeared before the 175-member board on Saturday in Washington, shortly before the vote on the endorsement. “There were a lot of undecideds when she started that conversation,” Eskelsen García said in an interview later that afternoon.

Eskelsen García, who had already conducted a videotaped sit-down interview with Clinton and the other candidates as part of the NEA endorsement process, believed that undecided board members would benefit from hearing from Clinton directly. Clinton, said Eskelsen García, was more than willing. “She said, ‘I’ll be there.'"

Clinton faced an hour of questioning. When it came time for the vote, she secured support from 75% of the NEA's board members — clearing the 58% needed.

Eskelsen García noted that all three candidates vying for the NEA’s endorsement — Clinton; Sanders; and Martin O’Malley, the former governor of Maryland — were well in line of the teachers union on the issues. But Eskelsen García said Clinton's lifelong commitment to public education "set her apart," citing her work for the Children’s Defense Fund and her 1993 effort to pass a universal health care plan.

“I think what happened is that after she left the room today, they were sure,” said Eskelsen García. “They said, ‘She’s the candidate who has made our cause the cause of her career.’”

The 175 people who sit on the NEA’s board work for public schools, colleges, and universities across the country, and include teachers, librarians, and bus drivers, said Eskelsen García. At the board meeting on Saturday, Clinton answered questions on “with precision,” said Eskelsen García. Clinton “could talk chapter and verse” about topics ranging from special education law to historically black colleges, she said. “People looked at each other and said, ‘She gets it. She understands it.’”

The vote comes as several other major unions have delayed an endorsement. Some labor leaders have said they would like to wait until Vice President Biden decides whether or not to get in the race. (Biden’s decision is expected this month.)

Those unions include the Service Employees International Union, and more recently, according to a report in the New York Times on Friday, the International Association of Fire Fighters, or the IAFF. A Clinton aide would not confirm the details of the Times story, which reported that the IAFF recently called Clinton’s campaign manager to withdraw an expected endorsement. The endorsement had never been guaranteed and remains on the table, a Clinton aide said on Saturday.

“As a lifelong fighter for children and families,” Clinton said in a statement on Saturday, "I am deeply honored to have earned the endorsement of the National Education Association and their nearly 3 million members."

The NEA represents a significant block of voters, totaling 3 million members and 5 million when including spouses and families. The endorsement follows the early support Clinton received in July from another leading union, the American Federation of Teachers, headed by a longtime Clinton backer, Randi Weingarten.

The NEA has made endorsements in every presidential race since the 1976 election, with the union participating in only some presidential primaries. In 2008, as Clinton competed against Barack Obama, the NEA opted out of a primary endorsement. The union’s decision to make an endorsement in the 2016 primary came only after a “powerful” debate among its members, said Eskelsen García.

From there, the NEA invited 24 candidates, including Democrats and Republicans, to participate in the union’s endorsement process. Only Clinton, Sanders, and O’Malley responded, completing a questionnaire and sitting for the videotaped interview with Eskelsen García.

In recent months, some NEA leaders have voiced support for Sanders, including in his home state of Vermont, where the union’s local chapter made an endorsement in June. “We want to let the whole country in on what we in Vermont have long known,” the state NEA president said at the time. O’Malley, the former governor of Maryland, is also close to the union and its members, winning the NEA’s Greatest Education Governor Award in 2010.

“It’s accurate that there are very passionate supporters on all sides,” said Eskelsen García, when asked about a rift in the NEA’s membership. “This was hotly discussed and debated... We understand that our members are going to have their hearts with certain candidates.”

On Thursday, the NEA’s political action committee, the NEA Fund for Children and Public Education, voted by 82% to recommend the Clinton endorsement. On Saturday, the board took that proposal up, issuing the 75% affirmative decision.

On Saturday afternoon, following the NEA vote, Sanders released a statement boasting the support of “hundreds of thousands of members of the National Education Association and trade unionists all across America,” he said.

“We are going to win this nomination and the general election because of support from grassroots Americans. We are on track to do just that.”