DeVos, a Michigan billionaire philanthropist, is a national figure on the cause of giving vouchers to parents so they can choose whether to send their kids to private or public schools. That is mostly a non-starter for Democrats. But the school-choice-above-all-else narrative also doesn't fit with some red-state Republican senators, whose rural states don't necessarily have a tonne of private or charter schools to choose from.
"If you are a senator who disagrees with DeVos on the issue of school choice and vouchers," said Elizabeth Mann of the Brookings Institution, "there aren't a lot of other places to find common ground."
2) She doesn't have experience in public schools
DeVos has not attended, sent her children to, or worked in public schools. And that's a big problem for people who see the Education Secretary's primary role as managing public schools, which a majority of American students attend.
"Like all of us, Mrs DeVos is the product of her experience," Collins said on the Senate floor explaining why she'd be voting against DeVos.
DeVos' viral confirmation hearing - where she seemed unfamiliar with basic laws and suggested guns in schools could help protect students "from potential grizzlies" - did nothing to assuage those concerns. And it even added a few more, like whether she'd support students with disabilities.
3) A united opposition, a split front of support
The increasingly nationalised debate over school reform has propped up a sizable, well-organised and often powerful coalition of labour and progressive groups that are opposed to DeVos' school choice position.
But it's not just teachers unions opposing DeVos. The Washington Post talked to parents across the country who opposed Devos and found them to be part of a surprisingly diverse group:
"[A] small army of parents, teachers and others around the country who have risen up against DeVos as President Trump's nominee heads toward a breathtakingly close confirmation vote. They come from places as diverse as rural Alaska, inner-city Detroit and ... suburban Nashville."
"Vouchers don't come with any oversight of the schools in which they're spent," Anna Caudill, a Tennessee mother-of-two, said.
Very few Cabinet nominees have such a built-in and well-organised opposition, said Frederick Hess, a DeVos supporter with the American Enterprise Institute. "I don't know who has that kind of mobilisation on the secretary of state, no matter how much more high-profile the position is," he said.
4) Senate Democrats are at war with Trump
Senate Democrats' unanimous opposition to DeVos is rare. For decades, the Senate's practice has been to give new presidents deference in their Cabinet picks. But nothing about Trump's presidency is normal, and Senate Democrats are making Trump's picks go through extraordinarily high hurdles to get approved.
Secretary of State Rex Tillerson was the first secretary of state nominee in US history to ever have to clear various procedural hurdles before a final confirmation vote.
Democratic senators have boycotted committee votes on Trump's nominees for Treasury, the Environmental Protection Agency, and health and human services, forcing Republicans to suspend the rules and advance the nominees without a quorum.
DeVos, for all the reasons listed above, provided Democrats the perfect opportunity to take their biggest stand yet against Trump. In the end, she got confirmed, but Democrats succeeded in making it one of the most contentious battles to date for a Cabinet nominee.