Doug Jones’ shocking victory over Republican Roy Moore in Alabama’s special election on Tuesday night will deal a devastating blow to what’s left of Donald Trump’s agenda in 2018. It will also put Senate Republicans’ majority in serious jeopardy beyond that. Jones is just one vote. But one vote in the Senate changes everything.

In the very near future, Jones’ win probably can’t stop Republicans from passing their tax bill. Jones will not be seated until the state of Alabama certifies his election, the deadline for which is Jan. 3. The Alabama secretary of state’s office told me Tuesday that they expect to complete certification between Dec. 27 and 29. Senate Republicans are aiming to complete their tax bill before they leave for Christmas, with a final vote next week. Jones’ win will only encourage them to wrap this up faster. Barring a collapse in conference negotiations, Jones will arrive too late.

The optics of Republicans racing before Christmas to pass an unpopular tax bill before they lose the requisite votes, though, won’t be pretty. Senate Democrats, by Tuesday night, had already begun taking their pound of flesh by calling on Republicans to halt the process.

And then there’s next year.

Just think of what congressional Republicans were considering bringing up in 2018. Some conservative senators were talking about giving Obamacare repeal another go, with a revamped version of the Graham-Cassidy bill they considered in September. That’s got to be off the table now, since there were already at least two hard “no’s” on that particular framework: Kentucky Sen. Rand Paul and Maine Sen. Susan Collins, both of whom now have increased leverage for their unique demands on a variety of issues. In the new Senate, two Republican defections will be enough to kill a bill.

House Speaker Paul Ryan and the Trump administration have also talked about tackling “welfare reform” next year, which could include a grab-bag of cuts to SNAP, Medicaid, any other program that provides assistance to poor people, and possibly Medicare. Is that something that Senate Republicans will be interested in taking up, in an election year, with only one vote to spare? What other partisan legislation were they considering that, facing a more likely death in the Senate, they’ll now abandon?

Not only is the Republicans’ partisan agenda dealt a near-fatal blow by Jones’ arrival, but the GOP now has its work cut out trying to retain a Senate majority in next year’s elections.

Prior to tonight, there was no obvious path for Democrats to win back the Senate in 2018. They needed to retain their two dozen in-cycle seats and win three more swing seats: Arizona, Nevada, and… where else? Tennessee, where Sen. Bob Corker is retiring and Democrats have fielded a former governor to run, had been a possibility. Or perhaps a long-shot upset of Texas Sen. Ted Cruz? Neither of those seemed obviously winnable. Now, Democrats don’t have to worry about picking up a long-shot. They just have to flip Arizona and Nevada.

Who knows what other tricks Mitch McConnell has up his sleeve in 2018, either legislatively or electorally. And defending two-dozen Senate seats still won’t be a breeze for the Democratic Party. But a year from now, we might look at tonight as the beginning of the end of Republicans’ unfettered partisan spree.