Republicans will maintain control of the House of Representatives, NBC News projects.
The GOP is seen taking 236 seats to the Democrats' 199, according to NBC's House Model.
Republicans were widely expected to hold the House and create a policy buffer in a possible Hillary Clinton presidency.
Still, the development proves all the more important for the Republican agenda — and the potential to block the Democratic policy slate — as the parties fight for Senate control and the presidency on Tuesday night.
Some believed the Democrats could have a chance to seize control of the chamber amid the peak of Donald Trump's woes in early October, but those chances looked to vanish as the presidential race tightened.
Still, the Republicans face questions despite retaining control. House Speaker Paul Ryan's leadership could be challenged.
Ryan has clashed with his party's standard-bearer during the campaign, most recently after the release of a leaked 2005 video that shows Trump crudely joking about groping women without consent.
Amid the subsequent backlash, Ryan told House Republicans he would no longer defend the presidential candidate and instead focus only on maintaining GOP control of both houses of Congress.
— CNBC's Jacob Pramuk contributed to this story.