Cory Booker had expected 10,000 people to turn out for the rally in downtown Newark that launched his presidential campaign, but on April 13, against a huge American flag draped across a building high above Military Park, he looked out on just 4,100 supporters. The turnout wasn’t the only thing that felt light that day. In his speech, Booker stuck to what has become standard Democratic stump fare as teacher unrest convulses districts throughout the country: Teachers are underpaid, schools are underfunded, unions are essential. He made scant mention of his signature issue as mayor of Newark, namely his controversial overhaul of its public school system and messy battles with the city’s unionized teaching force.

For a candidate who’s been among the most energetic and best-known advocates for education reform over the past two decades, the omission was striking—but there’s a still more compromising entry on Booker’s CV that’s even more out of step with the pro-union sentiments of today’s Democratic Party: an early ideological partnership with Trump Education Secretary and diehard proponent of school choice Betsy DeVos. Booker was a young Newark city councilor when Dick and Betsy DeVos brought him to Michigan to play pitchman for Proposal 1, a 2000 ballot question that would have made private school vouchers a right enshrined in the state constitution and competency testing mandatory for Michigan’s teachers. The DeVoses had already donated millions of their Amway fortune to the campaign to pass the measure, and when it came time to hold a debate on the issue in their hometown of Grand Rapids, not just any champion of school choice would do. “We wanted someone who wasn’t from the suburbs,” Dick DeVos told a local reporter.

That Booker, the son of two IBM execs, had grown up in the tony community of Harrington Park, New Jersey, didn’t seem to matter. He was dispatched to the aptly named Wealthy Theater in Grand Rapids to speak for the initiative. Officially, he was there at the behest of the Acton Institute, a local conservative think tank that combines classical liberalism with the prosperity gospel (Betsy DeVos served on its board). To argue against the initiative, the ACLU of Michigan had sent its legislative director, Wendy Wagenheim, who warned that school vouchers would decimate the state’s urban districts, though Booker wouldn’t be around to see the damage: “I’m not flying out to New Jersey when this is over, as he is,” Wagenheim pointed out. “I will be here after this decision is made.” Booker parried with arguments that would soon become standard conservative talking points: Voucher opponents, he said, always prophesied doom and gloom as they sought to defend a system that was failing many children. The money doesn’t belong to the system, but to parents.

Proposal 1 went down in a crushing defeat—Michiganders rejected it by a margin of 69 to 31 percent—but Wagenheim’s dire predictions came to pass anyway. Over the next decade and a half, Betsy DeVos and her GOP allies transformed the state into a school-choice laboratory, taking the argument Booker himself had voiced on stage at the Wealthy Theater to its logical conclusion: that if the money belongs to the parents, not the school nor the system, parents should be the ones who get to decide where the money goes. Urban districts like Detroit, Highland Park, and Muskegon Heights imploded as charter schools proliferated and students fled, taking school funding with them. Amid this self-inflicted chaos, the state sent in “emergency managers”—another tactic seized by the DeVoses and the state business establishment as a blunt instrument to punish poor school districts, breaking them up and selling off their parts.

Booker’s Grand Rapids appearance marked the start of a relationship with Betsy DeVos that lasted more or less until politics intervened and he voted against her confirmation as secretary of education in 2017. “Somewhere in America, right now, there is a child who is wondering if this country stands up for them,” Booker proclaimed shortly after DeVos’s confirmation hearing, denouncing the woman who’d captained a school choice lobbying group, the American Federation for Children, that Booker had earlier credited as a principal cause of his political rise. Of course, Booker wasn’t alone among Democrats who’d embraced the gospel of school choice only to disavow its most prominent patroness. Colorado Senator Michael Bennet, who’d helped bring choice to Denver while at the helm of the city’s schools, also traversed a fine line at the DeVos hearings—and will have to again if he decides to run for president in 2020. But DeVos gave Booker a national platform, and bipartisan education reform kept him there.