Why are they so important?
The US elections on 8 November will have an enormous impact on the direction of the nation, as well as the fate of the person and the party in power in the White House.
Joe Biden is not on the ballot - the midterms decide who controls Congress as well as state legislatures and governor's offices. But the outcome will influence the playing field for the 2024 presidential campaign, and especially the odds of Donald Trump running again.
Here are five reasons why these elections are so important:
Abortion rights or restrictions
This is a textbook case for understanding how midterm voting can directly influence the shape of future policies and the day-to-day lives of Americans across the country.
In June the Supreme Court overturned constitutionally protected abortion rights. Both parties have already proposed new federal abortion legislation if they control Congress in the coming year.
Democrats promise to codify into federal law abortion rights that were protected by the Supreme Court's Roe vs Wade decision. Republicans have proposed a national ban on abortion after 15 weeks of pregnancy, a rule that would supersede existing protections in Democratic-run states like California, Illinois and New York.
Abortion rights will also play out in individual states, where the outcome of key governor and legislative races in traditional political battlegrounds like Pennsylvania, Wisconsin, Arizona and Michigan could directly determine the legality of the procedure in those states.
Joe Biden's future
Midterm elections are typically considered a referendum on the first two years of a presidential term - with the party in power often taking a beating.
Mr Biden's approval ratings have been poor for more than a year. While Democratic fortunes appear to have recovered somewhat, high inflation and concerns about the economy mean the party still faces an uphill battle to hold both chambers of Congress.
In his first two years as president, Mr Biden has managed to enact substantive legislation on climate change, gun-control, infrastructure investment and child poverty despite his narrow majorities in Congress. If one of those chambers switches to the Republicans, however, the window for accomplishment will slam closed for the rest of the president's first term in office.
A negative result will quickly be interpreted as a sign of Mr Biden's continued political weakness - and could renew calls for Mr Biden to step aside for another Democrat when the 2024 presidential campaign season begins.