Republicans now have only a one-seat majority in the Senate after Doug Jones' surprise victory in Alabama - here's what that means for 2018

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Donald Trump and Mitch McConnell

• Democratic Senate candidate Doug Jones was declared the winner in the Alabama Senate election on Tuesday night, cutting the Republican Party's majority there to just one seat.
• That election upset could cause problems for President Donald Trump and the Republican Party's legislative agenda going into 2018.
• Democrats are likely to capitalize on their electoral momentum to energize voters for the 2018 midterms.

Doug Jones' surprise victory in the Alabama special election on Tuesday night shrunk the Republican Party's Senate majority to just one seat, setting the stage for a potentially eventful 2018.

Jones, the first Democrat elected to the Senate in Alabama in more than two decades, could act as a roadblock to President Donald Trump and the Republican Party's legislative agenda, which, nearly one year into Trump's first term, has had precious little to celebrate aside from a Republican tax bill the passed in the Senate earlier this month.

That bill is now being debated in the House, where speaker Paul Ryan and other top party leaders are eager to put together a final bill for Trump to sign.

But that tax bill, much like other key planks of Trump's legislative agenda, are deeply unpopular, making the necessity of a congressional majority crystal clear for Trump. He has publicly acknowledged his need for GOP votes in his last-ditch efforts to stump for Alabama Republican Roy Moore, in what turned out to be an unsuccessful Senate campaign.

Earlier this year, Republicans failed in dramatic fashion in their efforts to repeal the Affordable Care Act - despite persistent prodding from Trump. One of those moments came in July when Sen. John McCain of Arizona went against his own party to cast the vote that killed a so-called "skinny" repeal.

Trump's proposed wall along the US-Mexico border has also seen little progress aside from contracts being awarded for border-wall prototypes. The president has frequently needled lawmakers who have been hesitant to appropriate funds for the wall, and has urged them to push forward his aggressive immigration agenda, often in the aftermath of terror attacks in the US and abroad.

With Republicans now holding just a one-seat majority in the Senate, and with GOP Sens. Jeff Flake of Arizona; Susan Collins of Maine; and Bob Corker of Tennessee positioned as wild cards there, Trump's legislative goals could face steeper challenges heading into 2018.

Beyond that, Tuesday night's election in Alabama - and Democrats' wave of electoral victories just last month in Virginia and New Jersey - have also set the stage for a potentially fierce midterm election next year.

But further Democratic momentum is not guaranteed. The party has 25 seats to defend in the Senate, compared to eight seats on the Republican side. In the House, where Republicans have held the majority since 2010, Democrats need to take back 24 seats to climb back over the top.