This turned out to be the year the teachers unions staged a comeback. Long on the defensive and losing members in Colorado and across the country amid expanding school choice and a rapidly shifting public education landscape, the unions dug in their heels. They opened their coffers and pushed back hard in Tuesday’s election against proliferating reforms like charter schools, performance pay, new accountability measures and in one district, school vouchers, all of which they have bitterly opposed.

And they regained a lot of ground:

A confluence of factors led to the union-driven victories.

Without a doubt, the deep pockets of the unions – the American Federation of Teachers, the National Education Association and their Colorado affiliates – played a pivotal role. Yet, that spending was matched and, in Denver Public Schools races, topped on the other side by well-heeled, pro-reform organizations and activists like Democrats for Education Reform and philanthropists Alex Cranberg, Pete Coors and Ed McVaney. In overwhelmingly Republican DougCo, the GOP played a big role in supporting the pro-reform board, too.

At least as instrumental in the gains of the anti-reform slates was an aggressive ground game. Organized labor’s inherent strength, after all, is organizing. And mobilizing. And it had a built-in network of motivated foot soldiers among teachers and other school staffers disaffected by reforms and, in DougCo, aggrieved at the loss of their collective-bargaining agreement several years ago at the hands of board reformers.

Also in play was the prevailing political climate in the era of the Trump presidency, which seeped into local board races to a degree that was arguably unprecedented. Particularly in decidedly Democratic Denver as well as in swing-voting Aurora, the polarizing president and his lightning-rod education secretary, Betsy DeVos, became bones of contention exploited by movement Democrats at the local level.

The war of words in the Denver races took on an almost ironic tone as candidates and their backers on each side – all registered Democrats – jockeyed for position as to who was more anti-Trump. Mailers and public statements, some the handiwork of independent committees, attempted to align pro-reform candidates – even board incumbent Barbara O’Brien, a former Democratic lieutenant governor and longtime liberal children’s advocate – with Trump administration education policies.

What’s the upshot of Tuesday’s potential game changer for some of Colorado’s largest school districts – and in some ways for the whole state?

One other thing appears certain: The fight over education reform will go on. Both sides have invested way too much – and believe there is too much at stake – to give up. And pro-school choice Democrats will be especially motivated to return to the fray. For them, it’s not only hard-won education reforms that are at risk but also the trajectory of their own party – a party whose last two U.S. presidents were committed advocates of charter schools.