(NewsNation) — The Republicans have won control of the U.S. Senate after the party flipped three seats in elections on Tuesday across the nation, NewsNation/Decision Desk HQ projects. See the results of the presidential election here. The Democrats have controlled the Senate since January 20, 2021, when President Joe Biden took office. Of the Senate’s 100 seats, the Democrats have occupied 47 while the Republicans have filled 49 entering Tuesday’s election. Despite the GOP filling more seats, the Democrats maintain a slim majority because of the caucusing status of four independent U.S. senators.  They include Sen. Bernie Sanders (Vermont), Sen. Angus King (Maine),  Sen. Krysten Sinema (Arizona) and Sen. Joe Manchin (West Virginia). Sanders, King, and Manchin all caucus with the Democrats while Sinema — a former registered Democrat — has said she won’t caucus with the Republicans, USA Today reported. Because of these alliances, the Democrats currently hold a 51-49 majority despite occupying fewer seats. Both Sinema and Manchin are not seeking reelection.  A total of 34 Senate seats were up for re-election on Tuesday with Democrats and independents representing 23 of those races.  Three of the most heavily watched races involving incumbent Democrats fall in key swing states that could determine the outcome of the presidential election.  In Michigan, Democratic Rep. Elissa Slotkin faced former Republican Rep. Mike Rogers to fill an opening created by the retirement of Democratic Sen. Debbie Stabenow. Ohio incumbent Sen. Sherrod Brown, the only Democrat to hold a statewide office in the Buckeye State, was locked into a toss-up race against Republican challenger Bernie Moreno, a businessman who has been publicly backed by former President Donald Trump. In Wisconsin, Democratic incumbent Sen. Tammy Baldwin was in another tight race with Republican investor Eric Hovde, who ran unsuccessfully for the Senate in 2012. Bloomberg reported that while the three swing state races remained among the nation’s most competitive, the push for Sinema’s open seat in Arizona also created another opportunity for the Republicans to gain an edge in a possible balance of power in the Senate.  Democrat Rep. Ruben Gallego, who has served five terms in Congress, was hoping to help Democrats maintain control of the seat against Republican Kari Lake, the former Phoenix television news anchor and former gubernatorial candidate. Manchin’s retirement from the West Virginia Senate seat he has held for 14 years was expected to create one opening for the Republicans, who are looking to flip enough seats to regain control of the chamber.  Jim Justice, West Virginia’s two-term Republican governor, built and maintained a big lead over Wheeling Mayor Glenn Elliott, which was expected to all but guarantee a Senate victory for the Republicans. In addition to the issue of which party controls the Senate, the chamber’s leadership could also shift depending on the election’s outcomes.  Democratic Sen. Chuck Schumer has served as Senate majority leader since the Democrats took control in 2021. Schumer is not up for re-election but would likely become the Senate minority leader should the balance of power shift to the Republicans. The GOP’s leadership within the Senate will also shift as longtime Kentucky Sen. Mitch McConnell announced earlier this year that he will step down as minority leader.  A trio of candidates have emerged as a possible successor to McConnell, headed by South Dakota Sen. John Thune, the Senate Republican Whip as well as Texas Sen. John Cornyn and Wyoming Sen. John Barrasso.