Vice President Mike Pence administers the oath of office to Sen. Susan Collins, R-Maine, as her spouse Thomas Daffron holds a Bible, during a reenactment ceremony in the Old Senate Chamber at the Capitol in Washington, Sunday, Jan. 3, 2021. Credit: Kevin Dietsch / Pool via AP

Two high-stakes Senate runoff elections in Georgia will determine the balance of power for the next two years, with implications for President-elect Joe Biden’s capacity to enact his agenda as well as the extent of Maine Sen. Susan Collins’ influence as she begins a historic fifth term.

Collins, perhaps the most moderate member of her party and with a long friendship with Biden, seems well-positioned as a dealmaker in the next two years. But her exact role will depend on whether Republicans maintain a narrow majority — in which case Biden stands little chance of passing any legislation without her support — or if Democrats take the majority, leaving her to negotiate from a minority position.

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Democrats must win both of the Senate elections on Tuesday to gain the Senate majority. In that scenario, the Senate would be equally divided 50-50 with Vice President-elect Kamala Harris serving as a tie-breaker for Democrats. Democrats already secured a narrow House majority and the White House during November’s general election.

Even a closely divided Democratic Senate likely won’t guarantee Biden everything he wants, given Senate rules that require 60 votes to move most major legislation. For measures that require a simple majority vote, Democrats would need every member of their caucus, including Sen. Joe Manchin, D-West Virginia, the most conservative Democrat in the Senate and a Collins ally, and Sen. Angus King, the Maine independent who caucuses with the Democrats.

But if Democrats lose even one of Tuesday’s contests, Biden would have little shot for swift up-or-down votes on his most ambitious plans to expand government-backed health coverage, strengthen the middle class, address racial inequality and combat climate change. A Republican-controlled Senate also would create a hard path for Biden’s Cabinet picks and judicial nominees.

In a scenario where the runoffs end in a split outcome, leaving Republicans with a 51-49 majority, Collins could play an outsized role, particularly in the confirmation process. She has a track record of confirming most judicial nominees from presidents of both parties, and Biden might count on her vote to bring many appointments across the finish line.

If Republicans win both elections, the party will maintain a 52-48 majority in the Senate, forcing Biden to find a coalition of Republicans in the upper chamber to support any of his proposals. That group would likely include Collins, but other Republicans would need to be on board too.

The results of the Georgia runoffs could also have implications for Collins in a few years. The Maine senator’s latest campaign included the refrain that she was next in line to chair the Senate Appropriations Committee when Sen. Richard Shelby, R-Alabama, retires in January 2023.

But Collins will only become the chair if Republicans maintain a majority in the Senate after the 2022 midterms. The party faces a somewhat difficult map that year, with two Republican incumbents in swing states, Pat Toomey of Pennsylvania and Richard Burr of North Carolina, set to retire.

Republicans will also have to defend seats in Wisconsin, Iowa and Florida in 2022, while Democrats will try to hand onto seats in New Hampshire, Nevada and Arizona, and one of the Georgia seats will be up again. While either party will have a shot at controlling the Senate after the midterms, winning the Georgia runoffs would yield a slight advantage.

The Associated Press contributed to this report.