In the Senate today, a simple majority isn’t enough to pass a bill: 60 out of 100 votes are necessary to break a so-called filibuster by invoking “cloture” to end debate. Routine use of the filibuster is a modern and accelerating phenomenon. Democratic Senator Joe Manchin of West Virginia, who regards the filibuster as a permanent fixture worthy of protection, has seen the cloture rule invoked 1,050 times since he took office in 2011. Before that, the preceding 1,050 cloture motions took more than 30 years to accumulate. In the filibuster’s first 50 years, starting in 1917, cloture was invoked an average of less than once a year.
Because neither party can reliably elect enough senators to overcome a filibuster, modern American politics is trapped in a Zone of Legislative Death: more than 50 seats, enough to select a majority leader; fewer than 60 seats, not enough to pass legislation. This zone is extremely difficult to escape. We calculated just how difficult.
Senators are elected by popular vote, meaning we can determine how many voters each major party represents. We added up the votes cast in the most recent election of all 100 senators. The result is a national popular vote, spread over several years. In the current Senate, whose members were elected in 2016, 2018, and 2020, the 50 Democratic-caucusing senators, including independents Bernie Sanders and Angus King, received 52.4 percent of the vote, while the 50 Republican senators received 47.6 percent.
What share of the vote would either party have needed to reach a filibuster-proof 60 seats? By shifting the vote in each of the 100 elections by the same number of percentage points until Democrats or Republicans were ahead in 60 races, we found that Democrats would have needed to win 55.8 percent of the national vote. Republicans would have needed to win only 50.2 percent of the vote to escape the zone—barely a popular majority at all.
We found a similar advantage for Republicans in every year since 1980. The advantage, 5.6 percentage points in 2020, averaged 3.4 percentage points. No wonder, then, that Republicans support the continued use of the filibuster. They are always closer to overcoming it than Democrats, irrespective of their appeal to voters.
The graph above shows the Zone of Legislative Death as a white band. Within this band is plotted the actual Democratic 100-seat popular vote. The color of the dots on the right panel indicates which party ended up in control of the Senate. Only once since 1980 have Democrats had a filibuster-proof majority—for six months, between the Minnesota Democrat Al Franken’s election in July 2009 and the Massachusetts Republican Scott Brown’s election in January 2010. And during the entire four-decade period, the total Democratic vote percentage has stayed between 49 percent and 54.5 percent, always below the necessary 55.8 percent.
Although Republicans do not need as much support to achieve 60 votes, getting there is still nearly out of reach because they usually win fewer votes nationally than Democrats. (In fact, Republicans have never once achieved 60 seats in the period since 1980.) But exceptions to the filibuster rule have been carved out that allow two major Republican policy priorities: cutting taxes and confirming federal judges. For Republicans, then, the status quo gives satisfactory results. For Democrats, current levels of partisan loyalty and obstruction guarantee that virtually no other bills can pass. The net result is a system that preferentially blocks one side’s goals.
The Zone of Legislative Death has widened over the years. In the 1980s, the zone was, on average, 3.8 percentage points wide. Since 2010, it has widened to 6.4 percentage points. This gulf widened because individual states have become more strongly partisan, leaving fewer competitive Senate seats.
Setting aside the filibuster, the modern Senate is strongly anti-majoritarian. Since 1980, Democrats have won the 100-seat popular vote 18 out of 21 times. But they gained control of the chamber in only nine of those cases. Using our extrapolation method, we calculate that an evenly divided national popular vote in 2020 would have given Republicans 59 seats. This nine-seat bonus arises from the fact that many Democratic votes are packed into high-population states such as California and New York, whereas Republican votes are distributed more efficiently in low-population states such as Wyoming and South Dakota. The correlation between partisanship and population density has held for 60 years, and is unlikely to go away soon.
Reformers and their opponents both expect that statehood for the District of Columbia would help close this gap, because D.C. statehood would likely guarantee Democrats two additional Senate seats. But this change would trim only a small part of the nine-seat bonus for Republicans. Furthermore, the Zone of Legislative Death would not change in size. So although granting D.C. statehood would enfranchise nearly 700,000 people, the reasons for doing so have more to do with fundamental justice than with the consequences for political power.
Removing the Zone of Legislative Death is as easy as a simple rule change. The procedure for ending debate has changed many times, starting in 1806, after Vice President Aaron Burr proposed the ability to end debate by “calling the previous question,” creating a requirement for unanimous consent for a bill to move forward.* The modern filibuster arose in 1975, when senators were no longer required to take to the floor to block legislation. If the rules changed 46 years ago, they can change again. Currently, the three-fifths requirement is calculated using all 100 senators, whether or not they are present. But the rule could easily be altered to count only senators who are present for debate, compelling them to take a public stand against popular legislation. Senators could still filibuster by speaking in person on the floor, as the civil-rights opponent Strom Thurmond did in 1957—but they would have to do so in full public view.
The modern explosion in filibusters coincides with an era of bitter partisan division. Since the mid-1990s, control of at least one chamber of Congress has changed 10 times, and the presidency has changed parties four times. The minority party’s motivation to block action until it can regain power has never been greater. Whatever the Senate does, our analysis shows that until the current cloture rule is changed, partisan polarization can halt the passage of most new legislation for decades to come.
*This article previously misstated that Aaron Burr was a senator when he proposed eliminating the previous question motion, and the Senate followed his advice in 1805. In fact, he was vice president at the time, and the Senate adopted his suggestion the following year.