Washington DC - US voters are casting their ballots in the 2022 midterm elections that will have a powerful effect on the final two years of Joe Biden's presidency, shaping policy on issues from government spending to military support for Ukraine.

Eligible voters will determine the majorities in the US Congress, made up of the House of Representatives and the Senate – as well as deciding on numerous governorships and other important offices.

Voters may punish the Democrats, who currently control the White House and Congress, and it is common for the party in power to suffer losses in the midterms.

The Democrats have a lot to lose, however, with a slim majority in the House and a wafer-thin advantage in the Senate, where they only have control thanks to a rule that gives Vice President Kamala Harris a tie-breaker vote. Republicans only need to gain one extra seat to win control of the Senate.

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If the Democrats lose their majority in Congress, Republicans are likely to block the majority of Biden's policies until the next presidential election in November 2024.

According to opinion polls, the House of Representatives is likely to go to the Republicans. In the Senate, meanwhile, a close race is expected. However, polls don't always tell the full story.

Much of the focus on the Republican side has been on how many candidates supported by former president Donald Trump will enter office.

The result of the midterms therefore may have a major impact on the next presidential race, with Trump dropping hints that he'll embark on another run for the White House.

Biden has repeatedly warned against Republican candidates openly questioning or even denying election results.