Republicans are one seat away from winning control of the House of Representatives after several races called for them in the US midterm elections.
The party had expected a stronger showing in both chambers of Congress amid high inflation and poor polling for the Biden administration.
But the Democrats have managed to cling on to control of the Senate, and have had an unexpectedly strong showing in the House, although they are unlikely to keep their majority in the lower chamber.
The Republicans currently have 217 House seats after calls in California and New York.
However, if they do manage to secure the 218 needed for a majority, it is likely to be by the slimmest of majorities in the 21st century.
The boost to the Republicans tally came after its candidates Michelle Steel and Ken Calvert were re-elected. Their seats had been seen as more competitive thanks to redrawing of congressional maps.
Thirteen races have yet to be declared, though only a handful are seen as tight enough to break either way. The Democrats currently have 205 seats.
If the Democrats fail to protect their fragile majority, Republican Kevin McCarthy would be in line to replace Nancy Pelosi as speaker.
However, Republican party leaders are facing a backlash over a disappointing set of results, with a promised “red wave” in their favour failing to materialise.
Former US President, Donald Trump, has backed Mr McCarthy for speaker, but he still faces the prospect of wrangling with his party to guarantee he is voted to the post when the new Congress convenes in January.
Meanwhile, Mr Trump could announce another run for US president on Tuesday, according to reports, despite the disappointing midterm defeats and signs his hold on the Republican party is waning.
“Hopefully, tomorrow will turn out to be one of the most important days in the history of our Country,” he wrote on his social media network on Monday.
An announcement was expected at 9pm EST Tuesday (2am Wednesday GMT) from his club in Palm Beach.
Another non-consecutive campaign is unusual for any US president.
Only one president in US history has been elected to two nonconsecutive terms, Grover Cleveland in 1884 and 1892.