Pulling such a trifecta -- winning the White House and Senate, which Republicans have already done, and maintaining their control of the House -- would end the party's four years in the minority and propel them into dominating every branch of government in the United States.
A comprehensive congressional victory would mean Trump gets enormous support to enact his domestic legislative agenda and appoint justices to the powerful US Supreme Court.
"As more results come in it is clear that, as we have predicted all along, Republicans are poised to have unified government in the White House, Senate, and House," Speaker of the House Mike Johnson said early Wednesday in a statement.
"The latest data and trends indicate that when all the votes are tabulated, Republicans will have held our majority."
Democrats need to flip only four House seats to climb out of the minority, but Cook Political Report, which closely follows congressional races, concurred with Johnson.
"At this point, the most likely outcome is a GOP trifecta, including a continued narrow Republican House majority," the publication posted Wednesday on X.
The US Capitol is divided into the House of Representatives -- where all 435 seats are up for grabs -- and a 100-member Senate, which had 34 seats at stake this year. Congressional elections run alongside the presidential race.
While decisions on several House races are headed to overtime, Politico reported Wednesday that Republicans have secured 198 seats so far in their quest for the magic majority of 218, compared to the Democrats' 180.
On the Senate side, Jim Justice, the sitting Republican governor of West Virginia, delighted Republicans early in the night when he emerged as an easy victor in the race to replace retiring moderate Senator Joe Manchin, a Democrat who later became an independent.
Ohio then moved into the Republican column after longstanding Democratic Senator Sherrod Brown was defeated by Bernie Moreno, a Trump-endorsed businessman and son of a one-time high-ranking Colombian government official.
Fox News and ABC called the race for control of the upper chamber after Republican Senator Deb Fischer fended off an unexpectedly robust challenge from an independent in Nebraska.
"I look forward to working with President Trump and our new conservative majority to make America great again by making the Senate work again," Senator John Cornyn of Texas, a contender to lead the Republican majority from January, said in a statement.
The Justice and Moreno victories reversed the Democrats' 51-49 Senate advantage, and Republicans soon extended their lead with a flip in Montana. Other potential pick-ups include Senate seats in Nevada and Pennsylvania.
Huge power
Democrats were looking to mitigate Senate losses with gains in Texas and Florida, but conceded both as the incumbent Republicans notched easy wins.
If Republicans win all of the toss-up races, they'll end the election with 55 of the 100 seats, giving them huge power to usher through Trump's domestic agenda and judicial appointments.
In a first, two Black women will serve at the same time in the US Senate, following victories from Democrats Angela Alsobrooks and Lisa Blunt Rochester in Maryland and Delaware respectively.
Of the 2,000-plus Americans who have served in the upper chamber, only three so far have been Black women -- including Harris. Alsobrooks and Rochester will become the fourth and fifth.
Sarah McBride will be the first openly transgender politician elected to Congress after beating Republican John Whalen III to take a House seat representing Delaware.
