The special election Tuesday to fill an Alabama Senate seat is poised to have a major impact on both the Republican Party's ability to advance its sprawling tax reform bill and next year's midterm elections.
The election to fill the office vacated by Attorney General Jeff Sessions pits Republican ex-state Supreme Court Chief Justice Roy Moore against former Assistant U.S. Attorney Doug Jones, a Democrat.
As of 10:45 p.m., ET, Jones led the race with few votes remaining to be counted, according to NBC News.
Moore, 70, aims to leverage an endorsement from President Donald Trump to overcome negative reactions from voters to multiple accusations that he sexually abused teens when he was in his 30s. Moore has denied the allegations.
Jones, 63, hopes to become the first Democrat to win a Senate election in Alabama since 1992.
Recent polling has swung wildly between the candidates. A Fox News poll released Monday estimated that Jones had a 10-percentage-point advantage, while an Emerson College poll showed Moore with a 9-point lead.
Regardless of what the polling projects, Jones faces an uphill battle to win a statewide election in deep-red Alabama.
Here are the issues at stake if either candidate wins:
As a Democrat in an overwhelmingly Republican state, Jones would likely become one of the Democratic Party's most moderate senators. From gun laws to corporate taxes, Jones has signaled he would likely take more conservative stances than many of his progressive colleagues on an array of issues before the Senate.
A Jones win would also knock the Republican Senate majority down to a razor-thin 51 seats from an already narrow 52-vote majority. And nabbing a seat now would slightly ease the Democrats' daunting task of retaking the Senate in 2018.
It could also have more immediate policy implications. If Jones wins, he could help to sink one of the GOP's biggest policy goals: overhauling the American tax system.
"What I have said all along is that I am troubled by tax breaks for the wealthy, which seem to be, in this bill, overloaded," Jones said about the tax proposal last month, according to Politifact. "I'm troubled by what appears to be, ultimately, tax increases or no tax cuts for the middle class."
The GOP is currently using special budget rules that require only a simple majority vote in the Senate to push through its tax plan. With 52 seats currently, Republicans can lose two votes and still pass a bill with a tie-breaking vote from Vice President Mike Pence.
House and Senate Republicans aim to pass a joint tax bill by Dec. 22, before they leave for Christmas. Should Jones prevail in Alabama, it would only increase the urgency of doing so before the new year. There is no guarantee that Jones will oppose the tax plan, but other Democrats in red states that Trump won easily voted against the Senate's version of the proposal.
It will take the state of Alabama at least until Dec. 27 to certify the election results, according to the Alabama secretary of State's office. Jones most likely would not be sworn in until January, and after that, Republicans would only be able to lose one vote on the tax bill and still pass it.
Sen. Bob Corker, R-Tenn., already opposes the tax reform plan. Sen. Susan Collins, R-Maine, could also decide to vote against it once she sees a final deal between House and Senate negotiators.
Looking beyond tax reform, a 51-49 Republican majority would also make it tougher for Republicans to pass any other legislation next year on a straight party-line vote. Defections within the party sank Senate GOP efforts to partially repeal the Affordable Care Act earlier this year.
A Moore victory, on the other hand, could relieve pressure on Senate Republicans to finalize and pass a tax reform bill before the new year, allowing them more time to iron out details, like state and local tax deductions, which could make a big difference on whether or not the bill is ultimately popular with voters.
Absent any other legislative achievements in Trump's first year, Republicans will need to use the tax reform bill to campaign on in 2018, and for that, they'll need as many provisions benefiting individual middle-class taxpayers as possible.
While the election of a scandal-plagued candidate like Moore will present a number of political problems for the GOP Senate majority, when it comes to advancing Republican fiscal and tax policy priorities, Moore is a likely to be a solid vote of support.
"Lower taxes, smaller government, and less spending will reduce the deficit and enable economic growth and a truly 'stimulated' economy," Moore wrote on his campaign website. "We are being taxed to death while our businesses are failing and our economy continues to suffer."
— CNBC's Christina Wilkie contributed to this report.