Compared with most of the 20th century, it has become much more rare since 2000 for either party to accumulate a comfortable Senate majority of 55 seats or more. And yet, even as each party is operating with fewer Senate votes of its own, it has also become more difficult for the majority to win votes from senators in the opposition party for its key initiatives.
These two trends have produced a political environment in which the only plausible path for presidents to pass their major priorities is to achieve near- (or even complete) unity in their party.
In the years ahead, the turmoil evident in the Senate over Biden’s agenda may become more the rule than the exception, as both parties operate with extraordinarily little margin for error — and even the slightest cracks in the unity of the majority are magnified by the ferocity of lockstep opposition from the minority.
Under these pressures, the Senate is simultaneously growing more polarized and more paralyzed. That dynamic has frustrated both sides, but it likely constitutes a greater long-term threat to Democrats, both because they typically try to pass more legislation than Republicans, but also because the core trend driving the polarization — the increasing alignment of presidential and Senate outcomes in the states — tends to magnify Republican influence in the chamber.
By contrast, Democrats reached 55 or more Senate seats in every Senate from 1961 through 1980 but one (the only exception came in 1971); in fact, in six of those 10 Senates, Democrats held at least 61 seats.
The elevated margins Democrats enjoyed in the body from the 1960s until 1980 were undermined when the party lost its hold on virtually all of the Southern Senate seats in the region’s post-civil-rights realignment. But even after that advantage vanished, one side or the other still reached the 55-seat threshold seven times from 1981 through 2000. (Democrats did it four times, and Republicans three.) That reflected a more fluid political environment in which enough states could still swing between the parties to allow either side to accumulate a substantial Senate advantage when the national political current shifted in its direction.
That’s much less true today. Fewer seats seem genuinely at play because of the tightening relationship between the results in presidential and Senate contests. It has become increasingly difficult for candidates in either party to win Senate seats in states that usually vote the other way for president.
After that stark outcome, Democrats now hold 47 of the 50 Senate seats in the 25 states that voted for Biden; Republicans, in mirror image, hold 47 of the 50 Senate seats in the 25 states that voted for Trump. Pulling back the lens only sharpens the picture. In the six presidential elections since 2000, 26 states have voted Republican a majority of the time: The GOP now holds 45 of their 52 Senate seats. Over that same period, 23 states have voted mostly for Democrats: The party now holds 43 of their 46 Senate seats. Iowa, the final state, has split 3-3 in presidential races since then (while shifting sharply toward the GOP in the past two): Republicans hold both of its Senate seats.
This hardening underlying dynamic makes it difficult for either party to amass a comfortable Senate majority. Since “the Senate outcomes now line up with the presidential outcomes” and about half the states lean toward each party in presidential contests, “you get a pretty even balance in the Senate in the same way,” says Gary C. Jacobson, a University of California at San Diego political scientist who specializes in Congress. “So it’s hard to break out of that parity because there have not been a lot of Senate candidates who have shown the ability to win across party lines.”
Few ‘split ticket’ voters
The same correlation of presidential and Senate outcomes that makes it more likely that each party can scratch out only a narrow Senate majority also makes it less likely the majority party can attract enough support from the minority to reach the 60 votes required to break a filibuster.
One implication of this alignment is that the vast majority of senators are sent to Washington by voters who also supported presidential candidates from their same parties. That creates enormous electoral pressure on Democratic senators to vote with a Democratic president and against a Republican one, and vice versa for GOP senators. The pressure is especially acute in this modern era, when any president faces overwhelmingly negative job approval ratings from voters on the other side.
But, in fact, the maneuvering of Manchin and Sinema in the current budget fight actually shows how much Congress has changed since that earlier era — and why the role they are claiming is so diminished. In their heyday, the “split ticket” legislators of the earlier era represented a large enough share of the Senate to build meaningful bipartisan coalitions on a regular basis.
“I used to have a coalition of about 10 people from both sides of the aisle that we could work with,” Breaux told me. “They don’t have that anymore — on both sides. The moderates are in the minority on both sides of the aisle, and that’s why you are seeing the [conflict] we are seeing right now.”
Bigger problem for Democrats
That leaves Manchin and Sinema in a very different situation from the earlier deal-makers like Breaux or Nunn. That older generation could, at times, advance a positive agenda that built a majority coalition across party lines; the influence wielded by Manchin and Sinema is now almost entirely negative. They can block their own party’s ideas, but on virtually all issues they can’t create the bipartisan alternative they claim to seek.
“There is no one to deal with on the Republican side of the aisle; it just can’t be done now,” says Mann. “So all Manchin and Sinema can do is negative,” by forcing Democrats to scale back their plans.
But on balance these new patterns probably present a greater challenge to Democrats, for several reasons.
One is that they have a much broader legislative agenda than Republicans, whose priorities are centered on two goals — cutting taxes and appointing federal judges and Supreme Court justices — that under existing Senate rules can already be passed with simple majority votes. (Taxes can be cut through the reconciliation process and judicial appointments are exempt from the filibuster.) As long as the filibuster remains in place, a bigger share of the Democratic legislative wish list — everything from immigration to gun control and voting rights — requires 60 votes.
But that’s easier said than done. The final problem for Democrats is that the ceiling for the number of Senate seats they can win under normal circumstances — with centrist or liberal candidates — is probably slightly lower than for Republicans. Even though Democrats have won the popular vote in five of the six presidential elections since 2000, Republicans, as noted, have won slightly more states a majority of the time during that period — which gives them a small but significant edge in the battle for Senate control.
Moreover, in 2024, Republicans can reasonably expect to competitively challenge Democratic incumbents in at least four Biden states from 2020: Arizona, Georgia, Nevada and New Hampshire. In Trump states holding Senate elections, Democrats are likely to be competitive in the North Carolina open seat and might be able to contest Ohio and Florida — but their best chance for gains is further consolidating their grip on the Biden states by winning seats the GOP now holds in Wisconsin and Pennsylvania.
The filibuster debate
To many observers, those limited opportunities underscore the need for Democrats to improve their competitive positive in at least a few more states. It’s telling that the Senate seats they flipped in 2020 came not in states they had bombarded with late television advertising, but in Arizona and Georgia — states where they had invested for years in grassroots organizing that also lifted Biden to victory. North Carolina is a plausible next target for Democrats to add a Senate seat in 2022 with that strategy, but after that the options, particularly Florida and Texas in the Sun Belt or Ohio and Iowa in the Rust Belt, look more daunting.
“There’s no real room to build coalitions that give really any chance of overcoming a routine requirement of 60 votes to get anything done,” notes Mann.
Even Breaux, a centrist who built his Senate career on finding deals with Republicans, thinks Democrats need to end the filibuster for what he calls “constitutional issues” such as voting and abortion rights. The filibuster, he says, can encourage cooperation “when you have an aggressive middle on both sides, and you don’t have that now.” As a result, he believes “in getting rid of [the filibuster] for constitutional issues, like voting rights. We’ve done it for the Supreme Court and federal judges, so I guess you could do a limited carve-out for constitutional issues. That at least would help get some things done.”
As population continues to concentrate in the largest states, this partisan imbalance will likely widen. Without a change in the filibuster, that would allow states representing an ever-shrinking share of the national population to block legislative action supported by senators representing a clear majority of the country.
“The dynamic is that a smaller and smaller segment of the American electorate will control more and more seats in the Senate,” says Mann. “So that there will be, in my view, a distortion that is so great it puts into question the entire legitimacy of the Senate as a governing body.”