Washington ( CNN ) -- In the battle for the Senate , nine races will play a role in determining the balance of power . Democrats currently hold six of the seats while Republicans hold the other two , meaning that the Democrats must defend their territory -- a difficult task in a midterm election with a Democratic president who has low approval ratings . Here 's a short synopsis of the key races that Democrats are working to keep in their hands : . Alaska : Sen. Mark Begich is another freshman senator who is facing a difficult road to reelection . He won his last race by fewer than 4,000 votes in the red state . He is distancing himself from President Barack Obama and touting his pro-energy credentials . He could face one of three Republicans . Their primary is August 19 . Arkansas : This is one of the most Republican states in the country . President Barack Obama received only 37 % of the vote in 2012 and Sen. Mark Pryor is locked in a race with Rep. Tom Cotton , a Republican backed by both conservative and establishment elements of the Republican Party . Louisiana : Since her first Senate race in 1996 , Sen. Mary Landrieu has had a tough road to election . Now running for her fourth term , Republicans are still trying to unseat the centrist Democrat . This year she will face off against one of several Republican challengers , including Rep. Bill Cassidy , who is considered her biggest threat . Louisiana runs its elections a little differently . November 4 , Election Day for the rest of the country , is considered Louisiana 's primary . And if no candidate receives 50 % of the vote , a runoff takes place December 6 . Michigan : Long-time Sen. Carl Levin is retiring , giving Republicans their first chance to take a seat in Michigan since 1994 . Republican Terry Lynn Land is staging a competitive race against Democratic Rep. Gary Peters . House and Senate key races to watch . Montana : Cook Political Report categorizes this race as `` lean Republican . '' Sen. John Walsh is running as an incumbent , appointed to the seat after Max Baucus left to become ambassador to China , but that status is thin in the conservative state as he 's only been in office since February . Rep. Steve Daines is the likely Republican candidate . North Carolina : Sen. Kay Hagan is running for her second term . It 's still unclear who she will face in the November election as Republicans are battling it out for that party 's nomination . But her likely challenger is state House Speaker Thom Tillis . While she will have to run against her Republican opponent , she also will have to run against her public perception as she faces approval ratings of only 35 % , according to an April 8 High Point University/University of North Carolina-Chapel Hill poll . Iowa : Sen. Tom Harkin 's retirement opens the seat up to a possible Republican win . Rep. Bruce Braley will be the Democratic candidate and the Republican field is crowded . But if no GOP candidate obtains 35 % support in the primary , then the candidate is chosen by a conservative state convention . Republicans are also playing in Colorado and New Hampshire , which means they have multiple paths to retaking the Senate . But Republicans are defending two key seats that could make it more difficult for them to pick up the majority . Kentucky : Republican leader Mitch McConnell is in the race of his life . He is being attacked by the tea party wing of the party with a challenger , Matt Bevin , who he 's likely to beat in the May 20 primary . Then Democrats have a legitimate chance in the red state with their candidate , Alison Lundergan Grimes . Georgia : The current Republican senator , Saxby Chambliss , is retiring , leaving his seat vulnerable . Michelle Nunn comes from a family steeped in Georgia politics and is proving to be a viable Democratic candidate in this red state . Over on the GOP side , the candidates are beating each other up in a contentious primary and pushing each other further to the right , which could leave the primary winner bruised and too extreme for a general election electorate . Additionally , primary candidates must win more than 50 % of the vote to avoid a runoff . With the crowded field , a runoff is possible , adding another challenging element to Republican efforts to keep this seat . Complete 2014 midterms coverage .
Republicans must pick up six seats to win control of the Senate . The race is a rematch from 2014, when Republican Sen. Pat Toomey won by just 1 percentage point over Democrat Katie McGinty.