Why are there only two candidates on the debate stage?

To add more choices, think bottom-up not top-down

Ben Raderstorf

On Tuesday night, Kamala Harris and Donald Trump will square off on the debate stage. It’s going to be a big night for our democracy. We’ll have more analysis of whatever comes up next week. 

Before then, I want to take a step back and look at a simple question with a sort of complex answer. Why do we only ever have two candidates debating?

For as long as we’ve had general election presidential debates, there’s only been a third candidate on stage twice: John Anderson in 1980 and Ross Perot in 1992. Every other presidential debate has been a head-to-head between one Republican and one Democrat. 

Yet most Americans wish they had more options for president — is that possible? 

The short answer is “no.” The long answer is… “kind of yes.” The difference is in whether we think about things from the top-down or the bottom-up. 

The “spoiler effect” means we’ll likely always have two main presidential candidates

The harsh reality is we can’t simply add more choices from the top-down. There’s no way to snap our fingers and add more serious presidential candidates.

To understand why, we need to first think about elections as more than just popularity contests. They’re about policy.

And policy can be understood on a spectrum. True, most political scientists encourage us to acknowledge that this stuff is multi-dimensional — views on the economy, environment, foreign policy, immigration, social issues and so on don’t always line up, well, in a line. But for simplicity here, let’s boil everything down to a single spectrum, from left to right. 

So for any election, we can plot the candidates and the election results on that line.

Let’s start by imagining an election with only two candidates. Let’s call them Alicia and Brian. Brian is a little closer to most voters’ preferences than Alicia, and in this election, 55% of the voters vote for Brian. 

Brian wins. Simple. When there are only two choices, the candidate most voters would prefer typically wins. 

Now let’s throw a third serious contender into the mix and see what happens. 

Oops. Even though the third candidate, Connor, is closer to Brian on the issues (and a majority prefer one of the two of them), Alicia is the one who wins.

When there’s one winner, a third candidate almost universally harms the candidate they most agree with on the issues and helps the candidate they most disagree with. In other words, Connor’s decision to enter the race is all but assured to hurt the issues and priorities he cares about by electing Alicia. 

This is true regardless of what Connor’s views are! Let’s say he’s actually to Brian’s right flank, not to the center. Same story. He hurts the candidate he most agrees with and helps the candidate he most disagrees with. 

This is the spoiler effect. 

Connor spoils the election for Brian (or vice-versa, the effect goes both ways). An additional candidate hurts the candidate that they most agree with and helps the one they most disagree with.

Read the full piece here >>