Many people around the world will be closely watching who is elected to move into the White House on Tuesday: Democratic candidate Kamala Harris or her Republican rival, Donald Trump. But just how much power Harris or Trump will wield in office will in part be decided in the elections for the US Congress, where the entirety of the 435-seat House of Representatives and 33 of the 100 senators are up for vote.

Members of the House represent constituencies with roughly the same population size. They are elected every two years. The Republicans have held a narrow majority in the House of Representatives since the 2022 mid-term elections. Pollsters expect a close race between Republicans and Democrats this year.=

The Senate has two seats for every state. This means that a US state like Wyoming, with a population of less than 600,000 has as much influence in the chamber as California with its almost 39 million citizens. The 100 senators are each elected for six-year terms. However, representatives are divided into three classes, whose six-year terms are staggered, with one third of senators standing for election every two years. This year, class I senators will be up for election; who were voted into the chamber in the middle of Donald Trump's presidency in 2018.

Overlapping election cycles were enshrined in the constitution to maintain a certain stability, says Katja Greeson, the director of the Transatlantic Program at the Aspen Institute Germany. "The idea is simply that senators can pursue their legislative goals in the long-term instead of having to focus on election campaigns." Greeson told DW. That said, "I'm a bit skeptical as to whether this will be the case in reality — there is a permanent election campaign in the US."

Democrats' strategic disadvantage

In 2024, the Democrats have to defend 19 party-held seats, as well as four held by independent senators who generally ally with them. Of the 49 Republican senators currently in office only eleven are up for re-election, while the remaining 38 are still in the middle of their respective terms. The Democrats, therefore, have much more to lose.

With the increasingly polarized US political landscape, it has become less common for the electorate to vote for different parties in the presidential and congressional elections,  Greeson said. "Nevertheless, vote splitting could be decisive this year." She cites the state of Maryland as an example, which is considered largely pro-Harris at the presidential level. But the current Democratic Maryland senator is not standing for re-election, with moderate Republican Larry Hogan competing against Democrat Angela Alsobrooks for the seat. "He [Larry Hogan] is very popular in Maryland, and I definitely expect that there will be some voters who will vote for him, as well as Harris."

In Montana, polls suggest that Democrat Jon Tester could lose his Senate seat to Republican Tim Sheehy. Pollsters expect the closest race to be in Ohio, where Democratic incumbent Sherrod Brown and his Republican challenger Bernie Moreno are neck and neck.

In other states, however, the situation is much clearer. Well known Democrat lawmaker Adam Schiff, for example, can expect to be elected senator in California — he previously held a seat in the House of Representatives. And in the small state of Wyoming, Republican senator John Barrosso will likely secure a fourth term in office.

What this means for the new president

If Trump wins the presidential election, he could find himself dealing with a House of Representatives dominated by the Democrats, limiting his powers.

Another conceivable scenario is that Harris wins the presidency but faces a narrow Republican majority in the Senate. "It will be a setback for Harris if the Senate is Republican," Greeson told DW. "Then it would be extremely difficult for the president to fill important positions in the first few months — judges, cabinet members and ambassadors, for example, would have to be confirmed by the Senate." She added that "it is unusual, historically, for many of these appointments to be rejected, but we don't know whether a newly elected Senate would break with tradition."

Harris would also face challenges regarding environmental issues, support for Ukraine, the debt ceiling, and proposals to lower food prices and invest in housing. "She would then have to seek bipartisan compromises from the outset," Greeson said.

This article was originally published in German.