When a California judge struck down tenure and other job protections for teachers this week, Education Secretary Arne Duncan and Rep. George Miller (D-Calif.) both applauded, revealing fissures in the once-solid alliance between labor unions and the Democratic Party.

“It’s a pivot point but one that’s been coming for a long time,” said Charles Barone, a former aide to Miller who is policy director for Democrats for Education Reform, an advocacy group formed in 2007 that promotes many ideas opposed by unions.

On Tuesday, a Los Angeles judge ruled that tenure and other job protections central to union contracts violate students’ civil rights to an education under the state constitution as the worst teachers are sent into schools populated by poor, minority children.

Attorneys for the plaintiffs in the case, Vergara vs. California, called it a landmark decision and said they intend to challenge tenure in a state-by-state campaign.

A spokeswoman for Duncan said he supports giving tenure to teachers who measurably help their students learn but that California’s policies did not give allow for meaningful assessments.

As Duncan and Miller celebrated the ruling, other Democrats attacked the verdict.

“If critics of teacher unions are concerned about the quality of education students may be receiving, then we should be doing more to provide teachers with opportunities to enhance their skills, not strip them of their workforce protections,” said Rep. Mark Takano (Calif.), a former teacher who received $10,950 from the National Education Association in 2012, making the union the third-biggest donor to his congressional campaign.

American Federation of Teachers President Randi Weingarten sent a sharply worded rebuke to Duncan on Thursday.

“You added to the polarization,” Weingarten wrote in a letter to Duncan. “And teachers across the country are wondering why the secretary of education thinks that stripping them of their due process is the way to help all children succeed.”

In California, the divisions within the Democratic Party are on display in the race for state school superintendent.

The incumbent, Tom Torlakson, a Democrat, is a former legislator with strong union backing. Torlakson, who was named as a defendant in the Vergara case along with Gov. Jerry Brown (D), said after the ruling that “teachers are not the problem in our schools, they are the solution.”

Brown has declined to comment on the ruling.

Torlakson is being challenged by another Democrat, Marshall Tuck, who was president of Green Dot, a chain of public charter schools. Green Dot is one of a few charters with unionized teachers.

Tuck sided with the plaintiffs, calling the state’s teacher protections “a broken system.” He and Torlakson will face off in November.

Jeffrey Henig, professor of political science and education at Columbia University’s Teachers College, said fractures within the Democratic Party over education policy began in earnest with the 2002 No Child Left Behind Act.

The signature education law of President George W. Bush was written in part by Miller and the late Sen. Edward M. Kennedy (D-Mass.) despite opposition from the teachers unions, which were against the law’s requirements for standardized testing and penalties for teachers and schools that did not make adequate academic progress.

The divisions have only grown with the Obama administration’s embrace of charter schools, the use of student test scores to evaluate teachers and other policies often favored by conservatives.

“The rift between the teachers unions and the so-called ‘New Democrats’ has been evident for some time,” Henig said. “Miller went off the unions’ favored course on No Child Left Behind, and Duncan has been at odds with the conventional union position almost down the line on charters, test-based accountability, etc. The Democratic Party is more internally divided on education than it is on most major issues.”

From New York Gov. Andrew M. Cuomo to Chicago Mayor Rahm Emanuel, high-profile Democrats have been battling teachers unions, a dynamic inconceivable a generation ago.

Miller said he does not favor eliminating tenure for teachers. “But the way the system is constructed in California is broken, and it needs to be fixed,” he said.

He said new laws are needed that protect teachers from arbitrary firings but also ensure that ineffective teachers are easily removed from the classroom. “I’m not saying it’s easy,” Miller said, “but it’s doable.”