(BSS/AFP) - Republicans nudged ahead in their mission to wrest the closely divided US Senate from Democratic control Tuesday after flipping a state and fending off an effort to unseat their most vulnerable members.

While all eyes are on the White House race between Democratic Vice President Kamala Harris and her Republican rival Donald Trump, hundreds of congressional elections will determine how much of the next president`s agenda gets enacted.

Jim Justice, the sitting Republican governor of West Virginia, emerged as an easy victor over his Democratic challenger in the Senate race to replace retiring moderate Joe Manchin, an independent who voted with the Democrats.

The US Capitol is divided into the House of Representatives, where all 435 seats are up for grabs -- and a 100-member Senate, which has 34 seats at stake this year.

As with polling in the White House contest, the congressional election looks close. Even with Republicans pressing their advantage in the upper chamber, control of the House was expected to be a toss-up.

Justice`s victory wiped out the Democrats` 51-49 Senate advantage, leaving Republicans needing just one more gain to take it back, and setting their sights on Montana, Ohio and possibly Wisconsin and Pennsylvania.

Democrats were looking to mitigate losses with gains in Texas and Florida, but conceded both as the sitting Republicans notched easy wins.

If Republicans win all of the toss-up races, they`ll have 55 of the 100 seats, giving them huge power to block Harris`s domestic policy should she prevail over Trump, and many of her appointments.

For the first time in history, two Black women will serve at the same time in the 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 Senate, only three have been Black women -- including Harris.

Nonpartisan political finance monitor OpenSecrets reports that $10 billion has been spent on candidates for Congress this cycle -- a touch less than in 2020 but almost twice as much as the $5.5 billion price tag for the 2024 White House race.

While the Senate approves treaties and certain presidential appointments like US Supreme Court nominees, all bills that raise money must start in the House, where the majority could take days to be decided.

The Democrats are in the minority, but overall control looks like a more realistic goal in the lower chamber, where they only need to flip four seats.

"The race for control of the US House remains as close as it`s ever been," said the Cook Political Report.

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.