As President Barack Obama and former Massachusetts Governor Mitt Romney enter their campaigns’ home stretch, they’ve been touring the country and delivering the same stump speech thrice per day for the past ten months straight. Both of the candidates read their words while looking out at the crowds, instead of down at a piece of paper, conveying the idea that they’ve memorized their speeches and are connecting with their audiences. And while conservatives take great pleasure in mocking President Obama’s reliance on a machine to help him deliver his speeches, the truth is that both candidates—along with politicians for more than a generation—read off of thin, nearly invisible plates of glass angled at a 45-degree slant at either side of their podiums. Perhaps more than any other technological advance—more than the touch-screen voting booth, the automated campaign phone call, or even the slick TV attack ad—the teleprompter continues to define our political age.

The device started out in 1948 as a roll of butcher paper rigged up inside half of a suitcase. Actor Fred Barton Jr., a Broadway veteran, was nervous. “For those that had been either in the theater or the movies, the transition to television was difficult, because there was a much greater need for memorizing lines,” says Christopher Sterling, a media historian at George Washington University. “At the time, there was a lot more live television, which many people today tend to forget.” Instead of memorizing the same batch of lines over the course of months, Barton was now expected to memorize new lines weekly or even daily. Cue cards were sometimes used, but relying on unsteady stagehands to flip between them could sometimes cause catastrophic delays.

Barton went to Irving Kahn, a vice president at 20th Century Fox studios, with the idea of connecting cue cards in a motorized scroll, so he could rely on prompts without risking an on-screen blunder. Kahn brought in his employee Hubert Schlafly, an electrical engineer and director of television research, and asked him if it could be done. “I said it was a piece of cake,” Mr. Schlafly told the Stamford Advocate in 2008. Using half of a suitcase as an outer shell for his new device, he rigged up a series of belts, pulleys, and a motor to turn a scroll of butcher paper that displayed an actor’s lines in half-inch letters. The paper was turned gradually, as controlled by a stagehand, while the words were read.

On April 21, 1949, Schlafly submitted a patent application for his “television prompting apparatus,” and in the tradition of offstage “prompters” who had been relied upon to feed forgotten lines to actors, he called his device the TelePrompTer. When the application was approved, the New York Times noted that it “coaches television actors into letter-perfect delivery of their lines and permits news commentators to simulate prodigious feats of memory.” It may have seemed unlikely at the time, but a new political age was born.

Although Schlafly, Barton and Kahn pitched the device to 20th Century Fox, the company was not interested. They promptly quit the company and started their own, founding the TelePrompTer Corporation. At first, the machine was used for its intended purpose: televised entertainment. It was part of a live production for the first time on December 4, 1950, as actors in the CBS soap “The First Hundred Years” read their lines off a device mounted to the side of the camera. “Initially, it was either above or below the lens of the camera or to the right or the left, so you could always tell, unfortunately, because you could see the person’s eye was slightly off,” Sterling says.

Quickly, others saw just how useful teleprompters could be—and as they began adding their own refinements, the term itself became a generic catchall for all sorts of automatic prompting devices. The TelePrompTer Corporation kept making their product, but many others began designing their own versions. Jess Oppenheimer, the producer of “I Love Lucy,” took out a patent for the first in-camera teleprompter, which used a system of mirrors and glass to project the script directly in front of the lens. “Once you could literally shoot through the teleprompter, the on-screen talent was looking straight at the audience,” Sterling says. “Home viewers saw a smoother presentation, with a hell of a lot more eye contact.” Soon, broadcast news operations started using the machine, replacing the printed scripts anchors had previously held in their hands, starting at the network level and then filtering down to local markets.

By the time the next presidential election rolled around, in 1952, Kahn saw the next frontier for his device. After reading that aging former President Herbert Hoover had had difficulty reading speeches while campaigning for Gen. Dwight D. Eisenhower, Kahn traveled to Chicago, the host city for the Republican National Convention, and persuaded Hoover and other speakers to try out the machine. The technology was an immediate hit—between that convention and the Democratic gathering later that month, 47 of the 58 major speeches were teleprompted. Two months later, though, candidate Eisenhower gave the technology an inadvertent publicity boost that allowed it to become legendary.