Even if Republicans win both races, they will control the Senate majority with only 52 seats. If Democrats win both, they will eke out a 50-50 Senate majority with the tie-breaking vote of incoming Vice President Kamala Harris. A split would produce a 51-49 GOP majority.
The fact that neither side will control more than 52 seats after Tuesday means that either party has held at least 55 Senate seats in only three congressional sessions since 2000. By contrast, in the previous 20-year span, one party reached 55 seats or more in seven congressional sessions. In fact, the meager three majorities of 55 seats or more since 2000 represent the fewest times that any party has accumulated at least 55% of the Senate seats over a 20-year span since the turn of the 20th century, according to official Senate records.
The inability of either side to build a big cushion has contributed to a historic level of volatility in Senate control, with neither party holding the majority for more than eight consecutive years since 1980, a span of turnover unprecedented in American history.
“The closeness of it, I think, is good for the center, and I think it’s good for Joe Biden because he’s a product of the center,” says John Breaux, a former centrist Democratic senator from Louisiana who is now a Washington lobbyist. Biden “understands the Senate. He grew up in the Senate; he knows that you have to talk to both sides. So I think the closeness of it — whether it’s 52-48 or 50-50 or 51-49 — is probably good for him and good for the country, because he is going to know how to deal in that type of a Senate.”
But other observers note that the narrow Senate majorities of recent years have, in practice, produced very few bipartisan compromises. Instead, they say the slim advantages — and regular shifts in control — have intensified the chamber’s growing partisanship. With control constantly at risk, the majority party faces heightened pressure for lockstep unity, while the minority party never has much incentive to help the majority burnish its record with bipartisan accomplishments that could buttress its advantage in the next election.
“Counterintuitively, narrow majorities are bad for bipartisanship, because when control of the majority is constantly within reach in the next election it gives the side that…