The 30-second campaign.

• Author: Smith, Patricia
• Position: NATIONAL

Even in the age of social media, TV ads still play an enormous role in presidential elections. Can they be trusted?

In one ad, a string of grim images of shuttered factories and struggling Americans are the backdrop for the ominous narration: "In Hillary Clinton's America, the middle class gets crushed." In the other ad, a series of dignified images of Clinton meeting with foreign leaders is followed by the narrator's reassuring message: "A steady leader in an unsteady world."

With ads like these, Clinton, the Democratic candidate, and Republican candidate Donald Trump are trying to present themselves to voters in the best possible light, while conveying unflattering--even frightening--images of their opponent. Like all advertising, political ads offer a biased point of view. Just as an iPhone ad is designed to sell iPhones, a political ad is designed to sell a specific candidate.

Americans are seeing a lot of political ads this fall--especially in battleground states like Ohio, Pennsylvania, and Florida. But voters everywhere are watching them--and debating them--on social media. That's because advertising plays such a key role in our elections.

"Old-fashioned TV advertising is tremendously important if for no other reason than most Americans don't pay very much attention to politics," says Erika Franklin Fowler of the Wesleyan Media Project in Connecticut, which tracks political advertising. "Campaigns are looking for ways to reach less-attentive citizens. One of the best ways you can do that is to reach citizens who are at home watching other programs."

Political advertising has been around since the mid-19th century. But in its early days, it consisted mostly of buttons, banners, and posters intended to generate turnout at local rallies and polling places on Election Day.

Ads on I Love Lucy

That began to change in the 1920s when radio's reach became widespread. But the truly seismic shift came with the arrival of television. In 1952, an advertising executive convinced Republican candidate Dwight D. Eisenhower that the sights and sounds of TV offered the quickest, most effective way to get his message across to voters.

His short commercials ran during popular shows like I Love Lucy and were a huge hit. Eisenhower's opponent, Democrat Adlai Stevenson, thought such ads were undignified and ran half-hour speeches on TV instead. (He lost, and in 1956, when he again ran against Eisenhower, he used TV ads, but lost anyway.)

In 1964, the campaign of President Lyndon B. Johnson, a Democrat, ran what's considered TV's first negative political ad. The "Daisy" spot capitalized on concerns that Johnson's Republican opponent, Senator Barry M. Goldwater, wouldn't rule out the use of nuclear weapons against America's enemies. The ad showed a little girl in a field, pulling petals off a daisy and counting up from one. Then her voice was replaced by an official-sounding male voice, counting down from 10 as a prelude to an atomic blast, which filled the screen with a mushroom cloud. The ad was so controversial that it aired only once.

Negative ads have been with us ever since. Even though most politicians claim to dislike them, the simple fact is that negative ads work, meaning they can influence voters to change their minds and affect a candidate's poll...