What's the Deal With the Senate?

America judges its presidential candidates in large part by the policies they pledge to enact, voting based on whose agenda they would rather see enacted. Yet there are a series of key races – those for U.S. Senate – that will determine whether Kamala Harris or Donald Trump will be able to truly rule supreme if elected to the Oval Office.

As it stands, Democrats hold a one-seat majority in the Senate, where Vice President Harris plays the tiebreaker: There are 47 Democrats (including Harris), four Democratic-leaning independents, and 49 Republicans comprising the Upper Chamber. The left is concerned, however, that the Senate will flip to GOP control come November: There are several Democratically held seats in red states that require defending and won’t be easy to hold.

Thirty-three of the 100 seats in the U.S. Senate will be contested in November. Of those, 26 senators (15 Democrats, nine Republicans, and two independents) are seeking reelection in 2024. Two Republicans, three Democrats and two independents – Kyrsten Sinema of Arizona and Joe Manchin of West Virginia – are not seeking reelection.

With Sen. Manchin retiring in a deep-red state, Democrats have essentially surrendered one seat to the GOP. If Trump wins in November, Manchin’s seat is all the Republican party would need to control the Senate.

For Democrats to hold the Senate, the party would need (1) all Democratic incumbents to win; (2) Democratic candidates to win open seats in Maryland and in the swing states of Arizona and Michigan; and (3) Harris to win the presidential election so that her running mate, Gov. Tim Walz of Minnesota, could play the tiebreaker in what would be an evenly split Senate.

There are two Democrats defending their seats in solidly red states: Sen. Jon Tester of Montana and Sen. Sherrod Brown of Ohio. Both men would need a significant number of split-ticket voters to support them in November, as Trump won both states handily in 2020 and will likely do so again this November. Tester trails by 5.2 points in the RCP Average while Brown leads by 3.6 points, according to the RCP Average. Cook Political Report rates the Montana Senate race as leaning Republican, while Ohio is considered a toss-up.

The other race Cook considers a toss-up is the open contest for the seat of Sen. Debbie Stabenow (D-MI) now that she is retiring. Rep. Elissa Slotkin is the Democratic candidate facing off against mainstream Republican Mike Rogers. Slotkin leads in the RCP Average by 5 points.

There are four races that Cook slots in the “leans Democrat” column: Arizona, Nevada, Pennsylvania, and Wisconsin. Notably, these are four of the seven key battleground states in the upcoming presidential election. Turnout for Senate candidates in these states will likely correspond to turnout for presidential candidates, as voters typically vote along party lines.

Democrats are playing offense in only two states: the reliably Republican Texas and Florida. The left is running candidates against Ted Cruz of Texas and Rick Scott of Florida, two men who have never been particularly popular. The Democratic candidates – Rep. Colin Allred in Texas and former Rep. Debbie Mucarsel-Powell in Florida – are doing as well as could be expected given their geographical handicaps. Still, it would take shock upsets to topple Cruz or Scott, who lead in the RCP Average by 6 points and 4.3 points respectively. 

The takeaway? The coveted federal government trifecta – single-party control of the House of Representatives, the Senate and the presidency – is an unlikely feat for Democrats, even if Harris does prevail in November.