Republicans took control of the Senate, the upper house of the US Congress, last night after winning seats held by Democrats, thus capturing the majority in that body after four years.
Democrats watched their efforts to save their slim majority slip away as the results favored Republicans.
Democratic efforts to oust firebrand Republicans Ted Cruz of Texas and Rick Scott of Florida have failed.
With control of the entire Congress at stake, the House and Senate contests will determine which party has the majority and power to bolster or block the president's agenda, or whether the White House faces a divided Capitol Hill.
The focus now turns to the "blue wall" Democratic states of Pennsylvania, Michigan and Wisconsin where Democrats are fighting to protect seats in what's left of their slim Senate majorities.
In the end, just a few seats, or just one, could change the balance of any home. With the Senate 50-50, the party in the White House determines the majority, as the vice president is the tiebreaker.
The key contests are taking place alongside the first presidential election since the attack on the Capitol on January 6, 2021, but also in unexpected parts of the country after one of the most chaotic sessions of Congress in modern times.
Voters said the economy and immigration were the top issues facing the country, but the future of democracy was also a driving force for many Americans voting in the presidential election.
The AP VoteCast, a wide-ranging survey of more than 110.000 voters nationwide, found a country mired in negativity and desperate for change as Americans faced a stark choice between former President Donald Trump and Vice President Kamala Harris.
Congress plays a role in maintaining the American tradition of the peaceful transfer of presidential power. Four years ago, Trump sent his hordes of supporters to "fight like hell" at the Capitol, and many Republicans in Congress voted to block the election of President Joe Biden. Congress will be called again to certify the results of the 2025 presidential election.
Parties and outside groups have spent billions of dollars on a narrow battle for both the 435-member House and 100-member Senate.
The races are focused on New York and California, where Democrats are trying to win back some of the dozen or so seats where Republicans have made surprise gains in recent years with strong lawmakers who helped bring the party to power.
However, the counting of votes could take some time this Sunday.
What began as a low-key race for control of Congress was instantly transformed when Kamala Harris stepped in to replace Biden at the top of the ticket, galvanizing Democrats with massive fundraising and volunteers that lawmakers said reminded them of the enthusiasm of the Obama era in 2008.
The fallout from redistricting, when states redraw their maps for congressional districts, also changes the balance of power in the House of Representatives, with Republicans set to pick up a few seats from Democrats in North Carolina and Democrats picking up a second seat in black-majority Republican Alabama.
Members of the House of Representatives face voters every two years, while senators serve a longer six-year term.
If both houses actually change party control, which is possible, it would be a rarity in history.
Records show that if Democrats take the House and Republicans take the Senate, it would be the first time both houses of Congress have flipped on opposing political parties.
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