Democrats are also on track to take control of the US House of Representatives in the US midterm elections, after flipping eight Republican seats in states including Kentucky, New Jersey and North Caroline and showing strength even in solidly conservative districts.
In Texas, Democratic state Representative James Talarico withstood a barrage of outside spending to defeat scandal-plagued Republican Attorney General Ken Paxton in a state that voted for Trump by 14 percentage points two years ago.
In South Carolina, pediatrician Annie Andrews became the first Democrat to win a Senate seat since 1998, a stunning victory over Trump's hand-picked candidate Darline Graham in a state that he carried by nearly 18 percentage points in 2024.
Andrews' win, along with Democrat Roy Cooper's win in North Carolina's Senate race, gave the party two of the four seats it needs to net in order to take control of the chamber.
The results also suggested that a Democratic wave was growing large enough to swamp even deeply Republican areas.
As it grew clear Republicans were in danger of losing their congressional majorities, Trump wrote on social media, "I wasn't on the Ballot and if I was, we would have won IN A LANDSLIDE! Thank you for your attention to this matter."
After the death of his ally, US Senator Lindsey Graham, Graham's sister Darline was appointed to fill his seat and Trump encouraged her to run for a full six-year term. But her political inexperience proved a liability.
While several television networks projected that Democrats would eventually win a House majority, most of the chamber's most tightly contested races had yet to be called.
"In sweeping and decisive victories, the American people have rebuked the depravity, corruption and incompetence of the man named President Donald J Trump," incumbent Democratic Senator Jon Ossoff, the projected winner in Georgia, told supporters at a victory party.
Ossoff is being touted as a potential 2028 presidential candidate.
Democrats held onto three House districts in Florida that Republican lawmakers had redrawn earlier this year, all of which backed Trump by at least nine percentage points.
Midterm elections are typically viewed as a referendum on the president, and that is especially true for Trump, who dominates attention like no other politician. Trump himself told his supporters to "pretend I'm on the ballot" and held dozens of rallies in the closing weeks.
According to exit polls half of voters nationwide said they saw the 2026 midterm elections as an opportunity to rebuke the president, and three-quarters said they are "angry" or "dissatisfied" with the way the country is headed.
In addition, 70 per cent of voters surveyed said they wanted Congress to provide more checks and balances on the president.
History is against Republicans: The sitting president's party has lost ground in Congress in all but two midterms since World War Two. Trump's approval rating is hovering near his career lows, with voters frustrated by war with Iran, higher fuel prices and wider affordability concerns.
Opinion polls show voters are most concerned about affordability and disapprove of Trump's handling of the issue. His tariffs on imports and his decision to attack Iran in February raised prices for consumers.
There are 47 US House races widely seen as competitive, according to a Reuters analysis of the leading election forecasters. If the other contests all proceed as predicted, Democrats would need to win only 13 of those races to secure a majority.
