When television became the principal tool for political communication, seekers of the presidency confronted a new challenge: They had to present themselves not only as plausible leaders of a world superpower, but also as visitors Americans would welcome in their homes.
Television made White House aspirants guests - invited or not - in our households, and they began dropping by at all hours. Between news reports, interview programs, talk shows, chats with late-night comics, and commercials, candidates are now unavoidable as they occupy our screens and seek our support.
Back in 1969, writer Michael J. Arlen called Vietnam the "living-room war." Today, because of television, the "living-room factor" plays an increasingly significant role in presidential politics. To a certain degree, the road to 1600 Pennsylvania Avenue goes through your residence.
Textbooks might describe national campaigns as contests of ideas, competing policies, and proposals charting the country's future. But those messages, by and large, come to us via our TV sets from candidates as concerned with how they dramatize themselves and their cause as with any wonkish prospectus or 12-point plan.
The "living-room factor" means someone campaigning for president needs to conform to the medium's theatrical values. Portraying oneself as a comfortably likable person is essential. Television creates a sense of intimacy between candidate and voter, and the political figure hopes to become a regular guest in the collective American household for the campaign season - and the next four years.
The trick in cultivating a successfully telegenic "image" involves marrying personal traits - the authentic self - with qualities that make one engaging or appealing. If a candidate seems to a viewer to be in command and wears well, an emotional connection develops, and that bond can prove significant in the voting booth.
Before television, Franklin Roosevelt's mastery of radio in his "fireside chats" staked out the living room as a place politicians could go to establish a direct rapport with the citizenry. The nation listened, and FDR gave voice, authoritatively and compassionately, to problems Americans faced in their lives and homes.
With its visual dimension, television magnifies the connection radio created. An early observer of TV's growing involvement in political affairs was author Joe McGinness. In his still-instructive account, "The Selling of the President 1968," Mr. McGinness chronicles how communication advisers to Richard Nixon transformed the former vice president, who had lost in 1960 to TV-savvy John Kennedy, into an image-oriented winner eight years later. Nixon's opponent, Vice President Hubert Humphrey, never found his footing on the new terrain of the political-media landscape.
"Television did great harm to Hubert Humphrey," McGinness noted. "His excesses - talking too long and too fervently, which were merely annoying in an auditorium - became lethal in a television studio. The performer must talk to one person at a time. He is brought into the living room. He is a guest. It is improper for him to shout."
As television expands with more channels and means of delivery, chances for candidates to pop up - and pop by - multiply. It's no coincidence that since 1980, the only presidents to be elected twice - Ronald Reagan and Bill Clinton - used television so effectively that even opponents had to acknowledge their skill.
Mr. Reagan could poke fun at himself, but he understood what mattered. Leaving the White House, he told an interviewer: "For years, I've heard the question: 'How could an actor be president?' I've sometimes wondered how you could be president and not be an actor."
Although George W. Bush and John Kerry seem inescapable on TV these days, the upcoming debates provide sustained comparison. Especially for undecided voters, the living room will become a critical precinct for taking the measure of each candidate. At its heart, the viewer's decision is deeply personal: Do I agree with what animates or drives each nominee? Which one seems more genuine and convincing? Whom am I most comfortable with as a national leader in troubling times?
Four years ago during the debates, historian Richard Norton Smith remarked (on TV), "There is a dynamic in this race right now and it can be summed up by the question of whether you want Al Gore in your living room for the next four years or whether you want George Bush in the Oval Office for the next four years."
Behind Mr. Smith's sage quip were concerns about Mr. Gore's stiff, know-it-all persona and a perception that Mr. Bush, though likable, lacked high-office gravitas. Resolving that dilemma - and the race itself - proved anything but simple in 2000.
But there's also a larger point. Winning the Oval Office can depend on how well candidates come across in our living rooms - and whether we want to keep welcoming them into our homes.
• Robert Schmuhl is professor of American Studies and director of the John W. Gallivan Program in Journalism, Ethics & Democracy at the University of Notre Dame. He's the author of 'Statecraft and Stagecraft: American Political Life in the Age of Personality.'