Senators and presidential campaigns

Six senators currently contending for the Democratic nomination for president. Left to right: Bernie Sanders, Kamala Harris, Elizabeth Warren, Cory Booker, Amy Klobuchar, Michael Bennet. (From public domain images.)

A sitting senator has never defeated an incumbent president.

This, in and of itself, is not a particularly remarkable fact, given that there have only been five cases in which a sitting senator challenged an incumbent president, and in one of those cases, the senator resigned from office before the election. However, it does reflect two persistent and statistically significant facts of American presidential elections.

• Incumbent presidents are often re-elected.
• Senators are usually bad at running for president.

The first fact is the well-known incumbency advantage. The second fact is less familiar to the public … and as a unique quirk of American presidential politics, it’s less clear why it is the case. (This paper is a good place to start.)

Who becomes president?

From 1788 to 2016, there have been 58 presidential elections. Most feature two major candidates, but a few feature three or four major candidates. For my purposes, I will count 124 major candidates, and organize them by their last position in government service prior to running (military or civilian).