Edison Research projected that incumbent Republican Senators Tim Scott in South Carolina and Todd Young in Indiana would win re-election.
Fox News projected Republican Rand Paul would win re-election in Kentucky and Democrat Peter Welch would win an open Senate seat in Vermont.
I blame the current administration for that," said Bethany Hadelman, who said she voted for Republican candidates in Alpharetta, Georgia.
A Republican Senate would hold sway over Biden's judicial nominations, including any Supreme Court vacancy, intensifying the spotlight on the increasingly conservative court.
Those concerns swayed even some Republican leaning voters like Henry Bowden, 36, an Atlanta lawyer who said he voted for a mix of Republican and Democratic candidates.