The Democrats' Senate campaign arm raked in $5.8 million in December, outraising the Senate GOP campaign committee as both groups prepare for crucial elections in 2018.

At the same time, the Democratic Senatorial Campaign Committee (DSCC) finished paying off the last of its election debt and is entering the New Year with $19 million in its bank account.

Politico first reported the DSCC's December fundraising haul.

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The committee's fundraising haul for the month and its cash on hand puts it ahead of the National Republican Senatorial Committee, which reported raising $3.4 million in December and ending the year with $15.3 million on hand.

Both groups are gearing up for a series of potentially pivotal campaign fights in 2018. While Democrats are hoping to make gains by capitalizing on President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE's low approval ratings, the party is fending off Senate challenges in more states than Republicans are.

Democrats are facing challenges in 10 states that Trump won in the 2016 presidential election.

Among the most vulnerable Democratic senators, according to the Cook Political Report, are Sens. Joe Donnelly Joseph (Joe) Simon DonnellyEx-Sen. Joe Donnelly endorses Biden Lobbying world 70 former senators propose bipartisan caucus for incumbents MORE (Ind.), Claire McCaskill Claire Conner McCaskillDemocratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally Missouri county issues travel advisory for Lake of the Ozarks after Memorial Day parties MORE (Mo.), Joe Manchin Joseph (Joe) ManchinBiden promises Democratic senators help in battleground states Senate leaders quash talk of rank-and-file COVID-19 deal OVERNIGHT ENERGY: House Democrats tee up vote on climate-focused energy bill next week | EPA reappoints controversial leader to air quality advisory committee | Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' MORE (W.Va.) and Tina Smith Tina Flint SmithThe Hill's Campaign Report: Trump and Biden vie for Minnesota | Early voting begins in four states | Blue state GOP governors back Susan Collins GOP Senate candidate says Trump, Republicans will surprise in Minnesota Biden promises Democratic senators help in battleground states MORE (Minn.), who took office last month after Sen. Al Franken Alan (Al) Stuart FrankenGOP Senate candidate says Trump, Republicans will surprise in Minnesota Peterson faces fight of his career in deep-red Minnesota district Getting tight — the psychology of cancel culture MORE (D-Minn.) resigned amid sexual misconduct allegations.

But GOP-held seats in Tennessee, Nevada and Arizona are all considered vulnerable in 2018, according to Cook.