The story goes that in the landmark first Kennedy–Nixon debate, in September 1960, many of those who listened on the radio believed Nixon had won. Yet most of the 70 million or so citizens who watched on television were sure Kennedy had prevailed. On that night, (between 9:30 and 10:30 Eastern time), our understanding of the power of the visual image in politics entered a new era.

Today, when every exchange can be repeatedly replayed and every nuance and gesture, however slight, can be analyzed and deconstructed, a candidate's nonverbal communication is just as important as anything he or she might say.

As Sens. Barack Obama and John McCain prepare for their third and final debate on Wednesday at Hofstra University in Hempstead, N.Y., they will both be acutely aware that this is their last chance to make a meaningful connection with voters at home, particularly those still on the fence. Trailing in recent opinion polls and supposedly more at home in a "town hall" style debate format (with an audience that asks some questions), Republican McCain was widely expected to come out swinging in the second parley last Tuesday in Nashville, Tenn. It was watched by a TV audience of over 63 million, some 10 million more than tuned in for the candidates' first debate, perhaps driven by the economic crisis.

McCain made passing reference to the fact that soon after both had won their parties' nominations, he had invited Obama to participate in a series of similar town hall encounters. The Democrat had declined at the time, arguing that the three presidential events organized by the Commission on Presidential Debates were sufficient. But if this was McCain's preferred arena, the prevailing opinion is that he failed to capitalize on any advantage, with Obama appearing equally comfortable in the open forum.

After their first meeting in Oxford, Miss., McCain took a lot of flak for what appeared to be his deliberate and, to some, contemptuous failure to look directly at his opponent during the 90-minute proceedings.

Public speaking coach Nick Morgan wrote that whereas both candidates acquitted themselves well, "Sen. Obama looked at his rival when he took him on. And when he wasn’t looking at McCain, he was looking into the camera, talking to America. Sen. McCain, on the other hand, looked like the cranky half of a dysfunctional marriage, the cross one who won't look you in the eye."

Although TV audiences for both presidential encounters so far have outdrawn the 2004 debates between incumbent Pres. George W. Bush and Sen. John Kerry (D–Mass.), it was this year's vice presidential debate that proved the big winner with TV audiences, attracting more than 70 million viewers.

During the much-anticipated confrontation between Alaska Gov. Sarah Palin and Sen. Joe Biden (D–Del.), Republican veep candidate Palin scored points for her direct approach, and eye contact with the home audience. Both candidates were praised for how congruent their nonverbals were with their overall message, but Palin's "folksiness"—and winks at the camera—may not have resonated in the way her handlers had hoped with undecided viewers.

Watchers of the final presidential debate may be interested to see if there is a gaff or a "gotcha" moment, like the one Democratic contender Lloyd Bentsen perfectly pulled off against Indiana Sen. Dan Quayle in 1988's VP debate when the Texas senator told the soon-to-be-elected GOP candidate that he was "no Jack Kennedy."

Ronald Reagan—"the great communicator"—even used his "there you go again" line in two campaigns: in 1980 against Democrat incumbent, Pres. Jimmy Carter, and four years later, as an incumbent himself against former Vice Pres. Walter Mondale, who also found himself on the receiving end of one of Reagan's best lines.)

A single nonverbal slip can leave candidates labeled as out of touch, distant—or worse, insensitive: Think then President George H. W. Bush when he inexplicably looked at his watch during a 1992 debate with Gov. Bill Clinton (D–Ark.) and independent Ross Perot; Vice President Al Gore when he sighed during a debate against GOP Texas Gov. George W. Bush in 2000, and; Massachusetts Democratic Gov. Michael Dukakis's seeming lack of emotion when asked about the death penalty in 1988.

No matter how the candidates perform on Wednesday, one thing's for sure: they will provide more material for the writers at Saturday Night Live.