The United States is heading into one of the most consequential midterm elections in decades. On November 3, all 435 House seats and a third of the Senate will be up for re-election, widely seen as the first major referendum on Donald Trump's second term.
A year and a half ago, Trump won a decisive victory over Democratic candidate Kamala Harris. His Republican allies also secured narrow majorities in both the Senate and the House, giving Trump the power to push through legislation and cabinet appointments with minimal Democratic interference. However, with his approval ratings slipping, Trump is pushing hard to keep Republican control of Congress.
With power at stake, both parties are fighting not just for votes but for the electoral maps themselves — where those votes will be tallied. In this visual explainer, Al Jazeera breaks down what happens during the midterms, how primaries work, and how the shape of district maps can favor one political party over the other.
What happens in the midterm election?
On November 3, nearly 244 million eligible voters will head to the polls in the US midterm elections. These elections will not choose a new president but will decide 35 Senate seats and all 435 House seats. Voters will also elect 39 state governors and state legislators.
The Senate, the upper chamber of Congress, has 100 seats, with each state having two senators regardless of population size. In nationwide elections held every two years in November, roughly a third of Senate seats are up for re-election because senators serve six-year terms and elections are staggered.
The House, the lower chamber, allocates seats to each state by population, totalling 435 members. All serve two-year terms and are re-elected every cycle. In 2024, the Republican Party gained control of the House with 220 seats to the Democrats' 215 — the narrowest majority ratio since 1930. It is this slim margin that makes the redistricting fight particularly critical.
What happens in the primaries?
Before the November midterms, each party must decide which candidates will run. These internal contests, called primaries, began in March and run through the summer, state by state. Primaries are especially critical in districts with a strong Democratic or Republican majority, where the winning majority-party candidate rarely faces serious competition in November. In most states, primary turnout can shape the ideological direction of both major parties long before November voters cast their ballots.
This Tuesday, six states held primaries: Alabama, Georgia, Idaho, Kentucky, Oregon, and Pennsylvania. The schedule of primaries leading to November 3 is shown in the accompanying visual.
