What does it mean to 'endorse' a presidential candidate?

In presidential election years, certain words pop up in our lookup data—words that get dusted off for a short while before receding from the news, put back in the closet until we need them again. These words, like caucus, presumptive, and electoral college, are generally used infrequently, but election years make them, for a brief time, favorites among our lookups.

Although "endorse" has been used in English for more than 600 years, the figurative meaning of “to approve openly” is much newer

But some words do the hard work year in and year out, rising in popularity during an election year because of a less common meaning that is temporarily prominent. Endorse is such a word. It carries a lot of meaning on its back, and for good reason: it comes from the Latin word dorsum, meaning “back.”

Dorsum is the root of dorsal, meaning “relating to or situated near or on the back especially of an animal,” as in dorsal fin. That literal meaning of “on the back” is also the origin of endorse, which has meant “to write on the back of a document” in texts going back to before 1400. (Endorsement followed endorse in the mid-1500s.) For centuries the word's meanings were restricted to ones that required a writing implement, with the act of endorsing involving a simple signature (as in “endorsing a check”), or a more elaborate note functioning, for example, as approval of a military promotion.

The figurative meaning “to approve openly” or “to express support or approval of openly and definitely” is a relatively modern development, dating to the 1800s. An early use makes reference to the nominating convention of the Democratic Party in 1844, but could easily be imagined as a line from election coverage today; only the names would change:

Col. Benton endorses Polk and Dallas, but almost directly denounces the Convention which nominated them.
—The Brooklyn Evening Star, 28 June 1844

Endorsements involving approval weren’t initially limited to political contexts; an early use by Ralph Waldo Emerson in 1847, cited in the Oxford English Dictionary, shows broader application, with ideas and authors enjoying endorsements as well:

This book of Montaigne the world has endorsed, by translating it into all tongues.

With its origins in binding legal documents at a time when the written word was precious and the tradition of written laws was being established in England, endorse has retained its strong meaning: putting your name behind a candidate means, figuratively, carrying that candidate’s record, reputation, and actions on your back.