Democrats' hopes of capturing the House run through parts of California and New York, where challengers overnight succeeded in flipping two Republican seats.

Laura Gillen unseated Republican US Representative Anthony D'Esposito to represent a section of New York City's Long Island suburbs and Josh Riley beat Republican US Representative Marc Molinaro in the state's Catskills region.

In Nebraska, centrist Republican US Representative Don Bacon held off a challenge by Democrat Tony Vargas in a liberal-leaning Omaha-area district.

Republicans' majority in the Senate will allow them to confirm Trump's appointments of cabinet members, judges and other personnel, though they will not have the 60 votes needed to quickly pass most legislation.

The other uncalled competitive Senate races are in Nevada, where incumbent Democrat Jacky Rosen led Republican challenger Sam Brown by 1.3 percentage points with 96% of the expected vote counted, and in Arizona, where Democrat Ruben Gallego was leading Republican Kari Lake by 1.7 percentage points with 74% of the expected vote counted.