On November 3, about 210 million registered voters will decide how much power Donald Trump has for the rest of his US presidency.

Trump is not on the ballot, but control of the United States Congress is. Made up of the House of Representatives and the Senate, Congress writes the country’s laws and controls federal spending.

In this visual explainer, Al Jazeera breaks down how the elections work, which races matter and what the results could mean for either party. What happens in the midterm elections? Held halfway through a US president’s four-year term, midterm elections decide the makeup of Congress.

All 435 seats in the House of Representatives and 35 of the Senate’s 100 seats are being contested, including special elections in the states of Florida and Ohio to fill the seats vacated by US Secretary of State Marco Rubio and Vice President JD Vance. Voters in 36 states will also elect governors. House members represent one congressional district each and serve two-year terms, while senators serve six-year terms. Midterm elections are also widely considered a referendum on the sitting president’s performance.

Since 1946, the president’s party has lost an average of 26.5 seats in the House and a handful in the Senate in midterm elections, according to Todd Belt, a professor of political management at George Washington University. Beyond Congress and governors, voters will also elect state legislators and local officials.

Nadia Brown, a professor of government at Georgetown University, said that while national elections get most of the attention, “It is important to remember that local politics is where most Americans interact with government.”She added that “It is the local propositions or referendums on ballots [that] will impact the everyday lives of people.”What is at stake in the House and Senate?

Republicans hold majorities in both chambers. Losing either would give Democrats the power to block legislation and launch investigations into Trump’s administration.

Democrats need to gain three seats in the House and four in the Senate to take control. A 50-50 split in the Senate would leave Republicans in control, because Vance can cast tie-breaking votes.

Belt said a Democratic victory could significantly limit Trump’s ability to pursue his domestic agenda.

“If Democrats take one chamber, all non-government funding legislation will grind to a halt,” he told Al Jazeera. How do House elections work? The House of Representatives is the lower house of the US Congress.

Its 435 members each represent one local district and serve two-year terms, so every seat is contested every two years.

Seats are divided among the states by population, based on the US Census conducted every 10 years. California, the most populous state, has 52 seats, while the least populous, such as Wyoming and Vermont, have one each. A party needs 218 seats for a majority.

Republicans currently control the House, with 218 seats to the Democrats’ 214, and one independent sits with the Republicans. Two seats are vacant, one last held by each party. The new House will be sworn in on January 3, 2027. The House races to watch Each district elects its own representative, and the party that wins 218 seats takes control, so a few narrow wins in close districts can decide the majority.

Belt estimates that about 35 House races could decide the majority. He predicts Democrats could gain about 15 seats, despite Republican redistricting that he says has given the party an advantage in nine additional districts.

“People generally vote straight ticket, meaning they will vote for all the candidates of one party, so this is likely to affect down-ballot races [as well],” he said.

A battleground district is a seat either party could realistically win. The graphic below highlights 12 of these key races to watch. How do Senate elections work? The Senate is the upper house of the US Congress.

Its 100 members, two from each state regardless of population, are elected statewide and serve six-year terms, with about a third of seats contested every two years.

This year, 33 seats are being contested in regular elections, alongside special elections in Florida and Ohio. Those two contests will fill the remaining two years of terms previously held by Marco Rubio and JD Vance. Of the 35 seats being contested, Republicans hold 22, and Democrats hold 13.

Republicans currently have 53 senators. Democrats have 45, and two independents sit with them, giving the Democratic bloc 47 seats.

Democrats need a net gain of four seats to reach 51 and take control. Republicans can keep control with 50 because Vice President Vance can break tied votes. The new Senate will be sworn in on January 3, 2027. The Senate races to watch To win the Senate, Democrats must hold the 13 seats they are defending and flip Republican-held ones.

In Georgia, Democratic Senator Jon Ossoff faces Republican Mike Collins. Michigan’s open seat pits Democrat Abdul El-Sayed against Republican Mike Rogers, while Democrat Chris Pappas faces Republican John Sununu for an open seat in New Hampshire.

Republican-held seats offer Democrats opportunities elsewhere. In Maine, Senator Susan Collins faces Democrat Troy Jackson, who replaced primary winner Graham Platner after he withdrew in July. North Carolina’s open seat pits Democrat Roy Cooper against Republican Michael Whatley.

Ohio, Alaska and Iowa are also competitive, while Texas and Kansas have drawn growing attention as Democrats look for more routes to a majority.

Although Democrats face a more difficult path to a Senate majority than to control of the House, the growing number of competitive races has increased their chances of winning the chamber, according to election analysts. What are the key election issues?

The cost of living tops voters’ concerns, with rising petrol prices, housing costs and healthcare coverage squeezing household budgets. Reproductive rights remain a major issue, while immigration and the state of US democracy are also on the ballot.

The US-Israel war on Iran and the rapid growth of artificial intelligence (AI)` and data centres have raised further questions about security, jobs and energy costs. Who votes in the midterms?

About 210 million Americans are registered to vote, nearly eight in 10 US residents aged 18 or older, according to USAFacts, a nonpartisan organisation that compiles government data.

California has the most registered voters, with 23.2 million, followed by Texas (17.4 million) and Florida (13.6 million). Together, they account for about 26 percent of all registered voters.

Wyoming (278,468), Vermont (459,455) and Alaska (603,310) have the fewest. How different groups plan to vote A Pew Research Center survey conducted from September 28 to October 4 found that 44 percent of registered voters backed the Democratic candidate in their district, compared with 36 percent for the Republican. Five percent support another candidate, and 15 percent are unsure.

Men are evenly split, with 42 percent backing each party, while women favour Democrats by 45 percent to 31 percent.

The graphic below shows how voting preferences differ by gender, race, age, education and party affiliation. US election voter turnout Fewer Americans vote in midterms than in presidential elections. Since 1944, average turnout has been about 42 percent in midterms, compared with 58 percent in presidential races. What happens if Republicans lose the House?

A Democratic House could block Republican legislation and use its committees to investigate the Trump administration. It would also hold the power to impeach the president, which only the House can do.

Control would also give Democrats leverage over government funding. Every bill needs approval from both chambers, so a Republican Senate could not pass laws on its own.

Belt expects a Democratic-controlled House to lead to more confrontations over federal spending, including the 12 annual bills needed to fund federal agencies. That raises the possibility of further government shutdowns, when funding lapses and many federal services stop.

Belt also believes that Trump could turn increasingly to foreign policy if his domestic agenda faces opposition in Congress.

“Traditionally, presidents facing divided government in their last two years pivot to foreign policy almost exclusively. I think the same will be true for Trump,” he said. What happens if Republicans lose the Senate?

A Democratic Senate could block legislation and reject presidential nominees, including federal judges, Supreme Court justices, cabinet officials and ambassadors.

That makes Senate control consequential beyond the next two years. Federal judges serve for life, shaping rulings long after a presidency ends.

The Senate also holds the trial if the House impeaches a president. Removing a president from office requires a two-thirds majority, a threshold neither party is likely to reach. Would winning both chambers give Democrats full control?

No. Trump would remain president and could veto legislation, and overriding a veto requires a two-thirds vote in each chamber.

Senate rules also require 60 votes to end debate on most legislation, though some budget bills can pass with a simple majority. A narrow majority therefore does not guarantee a party can pass its programme.

A Democratic House could open impeachment proceedings against Trump, who has already been impeached twice. However, removing a president from office requires a two-thirds majority in the Senate. Belt considers another impeachment unlikely.

“There will definitely be investigations,” he told Al Jazeera, but added, “There will not likely be another impeachment because Democrats tried that twice and Republicans rallied behind Trump.”

When will we know the results? Results will begin emerging after the first polls close at 6pm Eastern time (23:00 GMT) on November 3, but some close races could take days to resolve.

Election night results are preliminary. Final tallies can take days or sometimes weeks as officials count mail-in, provisional and other outstanding ballots before certifying the results, and the pace varies by state. “In some states, it may take up to a week or more,” Belt said.

Some contests may go further. In Georgia, if no Senate candidate wins a majority, the race goes to a run-off election on December 1.

Belt warned that early results could give a misleading picture of the outcome. Because Republicans have historically been less likely than Democrats to vote by mail, some states could initially appear to favour Republican candidates before later-counted ballots narrow or reverse their leads. This is known as the “red mirage”. In states that count mail ballots first, the reverse can happen. A delay in counting or a change in which candidate is leading does not, by itself, indicate electoral fraud.

The vote will decide who writes legislation, scrutinises the administration and controls federal spending, setting the balance of power for the rest of Trump’s term.