Scott Olson via Getty Images Democratic presidential candidate Sen. Elizabeth Warren (D-Mass.) and American Federation of Teachers President Randi Weingarten visit with striking Chicago teachers at Oscar DePriest Elementary School on Oct. 22, 2019.

Randi Weingarten, the president of the American Federation of Teachers, is expected to endorse Massachusetts Sen. Elizabeth Warren for president at a rally Saturday night in Houston, according to a source familiar with the endorsement.

Weingarten is backing Warren in her personal capacity. The 1.7 million-member AFT has encouraged local unions and members to support either Warren, Vermont Sen. Bernie Sanders or former Vice President Joe Biden for the Democratic nomination to challenge President Donald Trump.

The endorsement could provide a jolt of support for Warren, ahead of Super Tuesday, when voters will decided how to award roughly one-third of the pledged delegates to the Democratic National Convention. Warren is counting on a strong Super Tuesday performance in California, Texas, Massachusetts and elsewhere to make up for middling results in the early states.

The decision by Weingarten, who was a prominent backer of Hillary Clinton during the 2016 presidential primaries, is likely to frustrate some local affiliates and members who have chosen to back Sanders. Several AFT affiliates, most notably the United Teachers of Los Angeles, have backed the democratic socialist’s presidential bid.

“It’s a big deal that there’s a former special education teacher running for president,” Weingarten wrote in a Medium post explaining her endorsement. “Being a teacher means being fearless and flexible, loving and compassionate, hardworking and resilient, and dedicated and devoted to making life better for all kids and families. Being a teacher means having an innate understanding of the value of public education and what is needed to help all children succeed and to support all educators. Elizabeth Warren gets this.”

Many large national unions have been unable to reach a consensus on who to endorse in the crowded Democratic primary field. But Sanders has succeeded in winning the support of more local affiliates than any other candidate ― and, as of the end of January, the donations of more educators than any other candidate.

Weingarten has praised Warren in the past, calling the Massachusetts senator’s education plan “a game changer for our public schools and the 90 percent of America’s students who attend them.”

Warren has promised to name a former public school teacher as education secretary, and to increase K-12 education funding by $800 billion over the next decade using revenue from her proposed wealth tax on fortunes over $50 million. Warren also shares the AFT’s skepticism of charter schools and high-stakes testing.

The AFT, which also represents community college instructors, school nurses and teachers aides, is one of the two largest teachers unions in the country. The 3 million-member National Education Association is yet to endorse a candidate.

A major reason that most national unions have stayed out of the primary race thus far is a desire to move past the rancor of the 2016 Democratic contest between Sanders and former Secretary of State Hillary Clinton. During that primary, many major unions, including the AFT, endorsed Clinton early on in the race, eliciting a backlash from some rank-and-file members and locals who were more supportive of Sanders.

Whether Weingarten’s decision to endorse in a personal capacity, while still keeping the union formally out of the race, spares the union a similar backlash remains to be seen. Already there have been tensions inside the United Federation of Teachers, the AFT’s New York City affiliate and the largest teachers union local in the country, over whether and how to endorse a candidate. A group of UFT members largely sympathetic to Sanders has unsuccessfully sought, against the wishes of union leadership, to put an endorsement up for a membershipwide vote.

Liat Olenick, a Warren supporter and a member of UFT, welcomed Weingarten’s announcement.

“A big reason I support Elizabeth Warren is her education platform and my interactions with her around public schools,” Olenick said.

Olenick, a public school teacher and founder of the Brooklyn-based progressive group Indivisible Nation BK, had sought to meet with multiple presidential candidates about her idea of nominating a public school teacher as secretary of education. Only Warren’s team followed up, giving her face time with Warren during a visit to New York City in March 2019. A couple months later, Warren pledged to name a public school teacher to the top post and shined a light on Olenick as the inspiration for the promise.

The experience, Olenick maintained, “speaks to the culture of the campaign and the candidate.”

Kenzo Shibata, a Sanders backer and a member of the executive board of the Chicago Teachers Union, sounded mostly conciliatory notes, offering that Weingarten had a “right” to endorse in the race. (Though Sanders courted the famously militant CTU, it ultimately chose not to endorse in the primary.)

He couldn’t resist a dig at Weingarten though, whom he noted has expressed skepticism of “Medicare for All” legislation that would effectively eliminate private health insurance.

Warren continues to support Medicare for All, but she revised her plan in November to split the phaseout of private insurance into a separate bill that she would only pursue after the passage of a public health care option.

Although the change is a question of timing rather than substance, some Sanders partisans consider it a sign of Warren’s lack of seriousness about fighting for the policy under pressure.

As a result, Shibata suggested that Weingarten ― an open skeptic of ending private health insurance ― might have found Warren’s plan appealing.

“Elizabeth Warren is not a big proponent of Medicare for All at this point,” Shibata argued, despite Warren’s statements to the contrary. “So [Weingarten] found a candidate who matches her values, and more power to her.”

The Chicago educator and member of the Democratic Socialists of America suggested that he would prefer it if the AFT continued to stay out of the primary in an official capacity.

“If things kind of stayed as they were, folks would continue to work for and support the candidates they like individually,” Shibata said. “Anything shaking that up further would be very confusing.”

Notwithstanding her support for Warren, Olenick admonished the union to follow as democratic a process as possible if it decides to make an endorsement.

“I believe in democratic processes and I think that also makes unions stronger when more people are involved in decision-making,” she said. “I would be thrilled if the AFT endorsed Warren, but I would want it to be a process that is democratic and representative of members in the locals.”