Sen. Elizabeth Warren calls Betsy DeVos the “worst secretary of education we’ve seen.” Sen. Amy Klobuchar says DeVos “shouldn’t be in her job.” Beto O’Rourke’s take on DeVos: “We can do better.”

In the hunt for a presidential nomination, those Democrats and others are increasingly taking swings at DeVos as a way to energize supporters, jostle for attention and curry favor with the nation’s major teachers unions, which claim millions of voters among their members.

Over the last two months, candidates have gone after DeVos at campaign rallies, during TV appearances and in policy proposals. They have used her name to get a rise out of crowds at events from Las Vegas to Virginia. DeVos herself has become as much of an issue as any education policy, attracting more attention than most other members of President Donald Trump’s administration.

“When you look across the Cabinet, there really isn’t anyone else who has driven engagement at a personal level in the same way she has,” said Mike Spahn, a managing director at Precision Strategies, a political consulting firm that works with Democrats. “She’s the one who draws the most negativity.”

So far at least six candidates have publicly opposed DeVos, often as they offer their own pledges to support public schools and raise pay for teachers across the country.

Warren in particular has framed her friction with DeVos as a cornerstone of her 2020 campaign. In a letter to supporters this month, the Massachusetts senator issued a scathing rebuke of DeVos and promised that, if elected, she will put a former public school teacher in the nation’s top education post.

“I’ll just be blunt: Betsy DeVos is the worst secretary of education we’ve seen,” Warren wrote. “She and her team are up to their eyeballs in conflicts of interest. Instead of championing our students, they protect for-profit colleges that break the law and cheat them.”

Education Department spokeswoman Liz Hill did not immediately provide comment.

Others who have taken jabs include former Vice President Joe Biden, Vermont Sen. Bernie Sanders and Pete Buttigieg, the mayor of South Bend, Indiana. In Fredericksburg, Virginia, O’Rourke recently drew cheers when he asked, “Do you all think that we can do better than Betsy DeVos as secretary of education?” He answered: “I do too.”

While it’s uncommon for an education secretary to become such a focus on the campaign trail, education itself is often an important topic in presidential races. During the 2016 election, Americans in both parties agreed that education was among the most important issues alongside the economy, according to a poll by The Associated Press-NORC Center for Public Affairs Research.

Democratic strategists say it’s politically savvy to tap into the left’s outrage over DeVos and her proposals, especially her support for school choice, her proposed overhaul of federal rules on campus sexual assault, and her efforts to roll back a variety of Obama-era regulations. Some say focusing on DeVos also can help candidates stand out in a crowded field of 23 competitors.

“It’s kind of a goldmine. For Democrats, she is the face of an incompetent administration,” said Scott Ferson, president and CEO of the Liberty Square Group a political strategy firm in Boston. “I think Democrats are looking for somebody who isn’t just going to knock the president every time they speak, and DeVos is a good surrogate for the administration.”

Candidates have taken aim at the secretary as the nation’s two major teachers unions begin deciding who will get their endorsements. Both the National Education Association, which claims 3.2 million members, and the American Federation of Teachers, with 1.7 million, are seen as powerful political forces and recently began vetting candidates.