Democratic presidential candidate Sen. Elizabeth Warren (Mass.) attended an American Federation of Teachers town hall on Monday in Philadelphia. (Matt Rourke/AP)

One promised to spend $315 billion to raise teachers’ pay. Another vowed to hire a former public school teacher as U.S. education secretary. A number of them want to eliminate tuition at public schools and forgive a mountain of student loans.

They are the Democratic candidates seeking their party’s 2020 presidential nomination, and education is a hot topic among a good number of them in the field of 23. It is also potential trouble for some candidates whose past positions, once dominant in the party, have been losing luster in the era of Education Secretary Betsy DeVos.

American voters have long declared education an important issue but never prioritized education in general elections — at least not until the 2018 midterm elections. That’s when some races were won or lost — depending on your point of view — on education issues. Scott Walker lost his bid for a third term as Wisconsin governor to Tony Evers, a former state education superintendent who campaigned against Walker’s assault on public education.

A remarkable string of teacher strikes in states led by Republicans and Democrats started in early 2018 and put new focus on the issues affecting public schools. The strikes were not just about bolstering teacher pay and benefits but about winning new funding for schools sorely needing resources, and an effort to support the U.S. public education system, which DeVos once called “a dead end.”

Now, as they seek to win the votes of millions of members of teachers unions and secure the endorsement of those organizations, some Democratic candidates are throwing out big ideas for raising teacher salaries, creating free universal prekindergarten, rebuilding crumbling school buildings and fixing other problems facing K-12 public education and higher education. For example:

  • With a new report saying that teachers earned 21.4 percent less in weekly wages in 2018 than professionals with comparable educations, Sen. Kamala D. Harris (Calif.) made her first big campaign policy pronouncement a plan to boost teacher pay: spending $315 billion over 10 years. Julián Castro, a former U.S. housing secretary and mayor of San Antonio, just released a comprehensive education program, proposing a federal tax credit that would increase teacher pay by up to $10,000 per year.
  • Sen. Amy Klobuchar (Minn.) has proposed a $1 trillion infrastructure program that would include resources to rebuild crumbling school buildings.
  • Sen. Elizabeth Warren (Mass.) just labeled DeVos the “worst education secretary” in the 40-year history of the department and promised to hire for that job a former public school teacher “who is committed to public education.” She also was the first to come out with a major plan to relieve students of debt, which stands at $1.6 trillion nationally. She wants to spend $1.25 trillion during 10 years to eliminate the student loan debt of about 75 percent of those Americans who have it, paid for with a tax on the superwealthy.
  • Several candidates support making education free at public colleges and universities. Warren, Sen. Kirsten Gillibrand (N.Y.) and Sen. Cory Booker (N.J.) co-sponsored a Senate bill to create federal-state partnerships that would allow students to attend public colleges without taking on debt. Sen. Bernie Sanders (Vt.) is taking a different approach, seeking to spend $47 billion a year in federal money to eliminate tuition and fees for undergraduates at public colleges and universities.

Five candidates — Harris, Warren, Sanders, Klobuchar and Rep. Tim Ryan (Ohio) — have appeared at forums sponsored by the 1.7 million-member American Federation of Teachers, the second-largest teachers union, to talk about their education vision.

Education has been a complicated subject for Democrats in recent years. The Obama administration pursued policies seen by public education advocates as moving toward privatization of the public school system and more in line with Republican thinking.

Those policies included pushing states to expand charter schools — which are publicly funded but privately operated -— and to evaluate teachers by student standardized test scores, an assessment method frowned upon by experts. The Obama administration also gave millions of dollars to Teach For America, which places recent college graduates with little training into high-needs classrooms. Veteran teachers see that as a slap at their professionalism. It did not, however, support school vouchers and other programs that use public money for private and religious school tuition. DeVos supports those measures.

In 2015, the Obama education agenda was so disliked that congressional Republicans and Democrats joined to pass a K-12 education law that sent back to the states much of the federal power over education policy exercised by the education secretary at the time, Arne Duncan.

Joe Biden was Obama’s vice president, but it was Duncan who was pushing the agenda and who became a lightning rod for criticism. The 3 million-member National Education Association, the largest union in the country, called for Duncan to resign, and the AFT came close to making the same call. It remains to be seen whether Biden distances himself from the Obama education agenda.

House Democrats just approved legislation that would substantially cut federal funding for charter schools. The bill cited a 2018 report by the Education Department’s inspector general slamming the agency’s oversight of the federal Charter Schools Program. And it mentioned a new report by an advocacy group, the Network for Public Education, that said as much as $1 billion in federal money was wasted on charter schools that never opened or that closed because of mismanagement and other issues from 2009 to 2016.

Charter schools and the financial impact they have on traditional school systems was a focus of at least two of the teacher strikes this year (Los Angeles and Oakland). In Los Angeles, the teachers union won a commitment from the charter-friendly school board to support a temporary statewide moratorium on new charters.

Booker is the Democrat who may have the toughest challenge with education issues. He has aligned himself with key policies supported by DeVos, including support for charters and voucher programs that allow the use of public money for private and religious school tuition. Mother Jones magazine recently ran a story titled, “Cory Booker Has a Betsy DeVos problem.” As mayor of Newark, Booker was a strong supporter of market-based school policies, and in 2016, he attended a policy summit convened by DeVos’s American Federation for Children, which he called “an incredible organization."

Beto O’Rouke, a former U.S. representative from Texas, says he supports the public education system, but in the past expressed support for charters (and his wife works for an organization that advocates for the expansion of these schools and has opened at least one charter school).

Reuters quoted Norma De La Rosa, president of the El Paso Teachers Association in O’Rourke’s hometown, as saying: “We’re going to have to get a lot of questions answered by Beto. At this point, I would be wary and I think a lot of my colleagues are going to hit him hard on these points.”

Pete Buttigieg, mayor of South Bend, Ind., recently said during an appearance at Northeastern University that charter schools “have a place” in the education world and can be “a laboratory for techniques that can be replicated.” Charter critics note that most of what charter schools have tried has been used in traditional schools and that comparisons are unfair.

Some of the Democratic candidates say they support charters but want responsible oversight and growth. Ryan has been pushing for years in the House to pass legislation that would increase oversight of charter schools. In his state, Ohio, the charter sector has been as troubled as any.

That doesn’t mean Ryan opposes all charters, but, for that matter, neither does Randi Weingarten, president of the AFT. In fact, the union once opened a charter in West Virginia.

But union members are likely to be wary of candidates who do not put their policy focus on how to improve the public education system.

Harris has been trying to play down a 2010 California law she sponsored when she was the district attorney in San Francisco that resulted in the jailing of some parents whose children were chronically truant from school. She said recently the jailing of parents was an “unintended consequence” of the law, although the law was specific in its punishments. She also said if she had to do all over again, she would do it differently.