Control of the US Senate: What does history tell us about how much it affects legislative policy-making?

With the U.S. Senate evenly split between the Republican and Democratic caucuses — something that’s only happened three other times — two political science scholars at the USC Dornsife College of Letters, Arts and Sciences were inspired to study one of those periods. Their research regarding the Senate during the 1953–54 session of Congress, published in the American Political Science Review, examines a period of time when nine senators died and one resigned, flipping party control twice.

USC Dornsife’s Christian Grose, associate professor of political science and public policy, and Nicholas Napolio, a Ph.D. candidate in political science, share insight on their research and what it might tell us about today’s Senate.

The period you studied was particularly tumultuous for the U.S. Senate. What from your research surprised you the most? 

Grose: A couple of things stand out. First, conventional wisdom is that because the U.S. Senate is very individualistic, party control of the Senate isn’t that important to advancing a policy agenda. Older research also supports that belief, particularly compared to the U.S. House, where the controlling party rules almost everything. Our research from this period upends that notion by showing that even a one-vote margin of control changed not just the Senate’s policy agenda, but the outcomes. We find this to be true not just for the unusual period we studied, but all the way through the present day.

I was also surprised by the suddenness of the changes in the Senate and that so many titans of the upper house unexpectedly and sadly died in such a short time period. It’s a reminder that history is shaped by who lives, and who does not.

Napolio: It’s also true that the 1950s, unlike today, were a time of relatively little party polarization. With low polarization, you would think changes in control of the Senate would have little impact on policy outcomes. But even with that low polarization, we found that changes in party majorities actually resulted in big changes in policy outcomes.

For example, Republicans were poised to pass a significant antilabor law, but Democrats — as the result of a senator’s sudden death — were handed the majority they needed to defeat the bill. Since the parties are now so highly polarized, the effects of a sudden change in party control today would have even bigger implications for policy.

We’re not even a year into the current session of Congress. How likely do you think it is that the 50/50 party balance in today’s Senate will change before the 2022 election?

Grose: The current Senate has a lot of people of advanced age, and sadly, some have health problems. During the two-year session of Congress we examined for our article, nine senators died! Of course, death isn’t the only factor that could shift control: In the past, pivotal senators have resigned from office or switched parties.

Napolio: There’s no doubt that the Democratic Party’s hold on the Senate is tenuous. Since 1960, an average of one-and-a-half senators has died each two-year session. The past can only tell us so much, but with five senators over 80, 23 senators over 70, and only one under 40, the current U.S. Senate is the oldest in the history of the country. What’s more, the average life expectancy in the United States is currently about 78.

Considering how often the filibuster is used today, requiring 60 senators to pass any type of nonbudgetary legislation, how much of a practical difference would it really make if party control of the Senate shifts before the next election?

Napolio: There are a lot of Democratic priorities that can’t be filibustered and don’t require 60 senators. For example, since 2013, nominees to fill positions in the bureaucracy and the courts cannot be filibustered and only require simple majorities for confirmation.

If Democrats lose their one-vote majority, Republicans could block Biden’s federal judicial nominees or force him to nominate more conservative judges. Since federal judges serve for life, that could have a generation-long impact on the federal judiciary.

Grose: I completely agree. But just in case some folks don’t know, let’s define a “filibuster.”  A filibuster is when a U.S. Senator effectively threatens to talk indefinitely on the Senate floor to delay or kill a policy proposal. Today it takes 60 senators to stop a filibuster and move legislation forward.

Our research explains — contrary to other research specifically about the filibuster — how a party with just a one-vote majority still has meaningful power and advantages. For instance, a Senate majority leader has procedural tools, within the constraints of the filibuster, to kill or table items they don’t want to bring forward.

Right now, there is growing pressure on the Democratic majority to end the filibuster in order to pass the John Lewis Voting Rights Act and related bills. For that to happen, all 50 Democratic Senators and the vice president would have to agree to change the rules, illustrating the importance of a cohesive majority party.

USC Dornsife political science scholars Nicholas Napolio (left) and Christian Grose. (Photo: Jordan Carr Peterson.)

What’s your prediction if Democrats gain a Senate seat before the 2022 election? 

Napolio: The Democratic senator from West Virginia, Joe Manchin, has been in the news a lot because he has outsized influence over the party. He’s among the most conservative Senate Democrats and won’t automatically vote with his party.

If the Democrats gain a seat, Manchin’s influence would be diminished, but to advance the party’s policy priorities, they’d still need the support of the next most conservative Democrat, Arizona’s Krysten Sinema. Since she has expressed similar views to Manchin, a one-seat gain probably wouldn’t make much difference for decision-making on the floor of the Senate. There could be some changes in committee compositions though.

Our research shows that slight changes in numbers without changes in party control didn’t really have much of an impact.

Grose: Yes, whether you’re looking at the 1950s or the modern era, our research finds that changes in party control of the Senate are much more consequential than a marginal one-gain seat by the party already in control.

So how about if Republicans gain a Senate seat? Considering there will still be a Democratic president and a House controlled by Democrats, how much of a difference would that make?

Grose: Party control of the Senate would still make a big difference. With control of the Senate, the G.O.P. leader would use procedural tools to advance the Republican party’s agenda, just like the Democrats are doing now.

Though elections matter, it’s also interesting — and at the same time frightening — how unexpected events like the deaths of Senators can shape policy and remake history. In the 1950s, a Senator died and so did Republican hopes of reshaping labor law. The Republicans had a proposal to curtail the power of unions, but when Democrats took control of the Senate, that Republican priority was sidelined for the remainder of that Congress (and the G.O.P. didn’t return to it once they took control as new issues emerged on the agenda).

Napolio: I’d expect more gridlock and an even less productive Congress if the G.O.P. gets a one-seat advantage. The federal budget bill might not even pass if Republicans control the Senate. Under Sen. Mitch McConnell’s leadership, the G.O.P. is likely to block any judicial or executive nominee who’s perceived as too liberal for the party. That would probably include all of Biden’s first picks for judges and other appointees, hamstringing other Democratic policy priorities.