Is Ronald Reagan or Bob Dole?
Or, more to the point, will McCain be perceived as the vigorous, wood-chopping proclaimer of "Morning in America" or as a cranky senior senator prone to gaffes and the occasional stage tumble?
The sensitive question of age - one of the trickiest and most unpredictable in the political playbook - has been touched upon only glancingly since McCain became the de facto GOP nominee. But it is certain to hover over a candidate who will be 72 by Election Day.
For all the ink spilled on whether the country is ready for a woman or African-American, polls indicate that more Americans worry about having a president over 70.
And McCain's public image is unmistakably tied to his age. Pew surveys taken in February and again last month showed that when voters are asked what word they would identify with McCain, "old" was far and away the choice.
Recent presidential history shows being a septuagenarian is not a disqualifier. Reagan was 73 in his 1984 reelection campaign and won a 49-state landslide.
Dole, however, was the same age when he ran for president in 1996 against Bill Clinton and was never really in contention.
Veterans of both campaigns agree that with McCain as the GOP nominee, age will again be an issue - and say the Reagan and Dole experiences offer the McCain team some best-case and worst-case scenarios on how to deal with it.
Ed Rollins, Reagan's reelection campaign chief, said campaign aides knew in the years leading up to the election that age would be an issue and prepared for it.
"We showed him as very active - lifting weights, swimming, riding his horse and chopping wood," Rollins said, recalling a Parade magazine cover story in early 1984 that detailed the president's workout regimen.
And as he did with many troublesome questions, Reagan used his own wit and impeccable timing to defuse the age issue. He invited the topic - and then promptly disposed of it by showing just how sharp he still was.
Ken Khachigian, another key aide in the Reagan reelection effort, recalled a speech Reagan gave during an Oktoberfest celebration in Milwaukee in September 1984.
Opening his remarks, Reagan said how great it was to be back at Old Heidelberg Park.
"I can remember when they called it just plain Heidelberg Park," Reagan said to laughs.
Later that fall, in his first debate against Democrat Walter Mondale, Reagan delivered such a weak, stumbling performance that real questions were raised about, as Khachigian put it, "whether the Gipper was losing it."
His staff, not helping matters, said the president had been tired.
"For a few weeks, the age issue really took off," said Bob Beckel, Mondale's campaign manager that year. After months of laboring to find an angle against a popular incumbent blessed with a growing economy and peace abroad, the Mondale campaign had a glimmer. "He finally gave us something," Beckel recalled.
And then he took it away.
With the is-he-too-old question on everybody's mind heading into the second and final debate, Reagan again deployed his humor.
Asked directly if he could still function in a crisis, the former actor nailed his line.
"I want you to know that also I will not make age an issue of this campaign," he assured, trying to be serious for the set-up. "I am not going to exploit for political purposes my opponent's youth and inexperience."
Even Mondale had to laugh.
Twelve years later, though, Republicans were grimacing, not laughing.
Dole was on his way to defeat, brutally defined by Clinton and his campaign team as a relic who could not be trusted to lead the nation into a high-tech future.
"Our line was 'Bilding a Bridge to the 21st Century,'" recalled Doug Schoen, one of Clinton's pollsters. "Anybody could see Bob Dole as being irrelevant for the 21st century."
To drive home the not-so-subtle message, Clinton cut what Schoen deemed a "negative bio ad."
Recounting Dole's decades in Congress, the Clinton team dredged up votes that were not only unpopular but redolent of a bygone era. "The message was: 'He was wrong from the start,' " said Schoen.
Dole didn't help himself, either. He referred to the Dodgers as playing baseball in Brooklyn; the team moved to Los Angeles in 1958.
And in September of 1996, he had what many political observers saw as a fitting moment for his plummeting campaign. Waving to supporters after a rally in Chico, Calif., Dole took a fall off the stage and had to be helped up.
For a middle-aged candidate, it may have just been good for a fleeting chuckle. But for a 73-year-old, it was the worst kind of imagery.
Democrats haven't been so lucky yet to have a Chico moment with McCain, but there are already traces of Clinton's rhetoric from the '96 race.
Before attacking his potential general election rival,always makes certain in his stump speeches to pay homage to McCain's patriotism - and longevity.
"John McCain has offered this country a lifetime of service, and we respect that," Obama said recently in Evansville, Ind., "but what he's not offering is any meaningful change from the policies of George W. Bush."
Obama's veiled language - the rhetorical equivalent of offering a gold watch - will apparently stay cloaked.
McCain's age is "not a topic we'll bring up," promised Robert Gibbs, Obama's top spokesman. "It's not his age that's an issue, it's his vision of a third George Bush term."
But some Democrats already have explicitly questioned McCain's fitness to serve at his age, including Rep. John Murtha, who himself is 75. The Clinton-backing Pennsylvanian has twice tweaked his fellow Vietnam veteran, suggesting first that the presidency was "no old man's job" and then that McCain's willingness to keep troops in Iraq for the long term was that of somebody who "doesn't expect to be around" for a second term.
Such shots, delivered by someone from McCain's own generation with a smile and a chuckle, are the way the issue can be exploited, said Beckel.
"The only people who can attack on this are his age or older," said Beckel, surmising that a contemporary could not be accused of ageism.
Trotting out a test line to be delivered by Murtha or another elder Democratic statesman, Beckel offered: "'I don't know about John, but at 73 I can't put up with that kind of pressure.'"
And, as Scott Reed pointed out, such an issue would have particular resonance among voters in the same age bloc.
"Seniors are the ones who really question [the age factor]," said Reed, Dole's campaign manager in '96. "And that's the voting group that really turns out in national elections."
Still, Beckel and others cautioned that using the issue against McCain would carry great risk.
"Attacking him personally about his age would have really driven our negatives," Beckel said of Reagan in the '84 race. Most political operatives have personally experienced the fallout that can come with trying to tar an opponent with the weight of his or her years.
McCain also has clear lines of defense. Just as the public had a degree of sympathy for Reagan's health after his shooting in 1981, Beckel noted that the injuries McCain sustained as a POW offer some protection.
The smarter course for the Democrats, Schoen said, is to hew to the subtler path.
"Obama ought to say: 'We're in a different world, in a different era, with different kinds of challenges.'"
And McCain should be prepared for it because the issue isn't going away, said Reed.
Unlike with race or gender, making light of old age is still fair game in American pop culture.
"You have to count on late-night comedians making it a mainstream issue," said Reed.
Recalling how careful they were about Reagan's schedule, Rollins had some advice for McCain: "Don't try to compete with him or you will break down," he said of the 46-year-old Obama.
And to McCain's staff, Rollins had this: "Make sure he's resting and eating - don't overextend him."
But that may be difficult given the very antidote McCain plans on using to deflect the age question.
"Watch me campaign," he shot back when asked about the matter at a conference of media executives last month in Washington. "Come on the bus again, my friends, all of you."
Another factor in addressing it, said adviser Charlie Black, is whom McCain picks for vice president.
Recalling the 1980 race, Black said the day Reagan tapped George H.W. Bush for the No. 2 slot the age issue "went away." Americans, said Black, recognized that Bush would be up to the task in the worst-case scenario.
"I think it will have a bearing," Black said when asked if McCain's choice would offer similar inoculation.
"We believe it will be ineffective issue," said senior adviser Steve Schmidt, noting that it had little impact in the primary. "He's got a lot of energy, he's in great shape, has kids in early 20s, and is very much attuned to popular culture."
Asked about Obama's tomorrow-versus-yesterday language, Schmidt said: "We have no intention of ceding who's the best candidate for the future to Obama. It's about the right kind change versus the wrong kind of change."
Should Obama get the nomination, though, it's almost certain to come up. And it likely won't matter if he raises it or not.
The 25-year difference between the two major candidates would be the most pronounced in the country's history and would be unavoidable should they be paired together on the debate stage this fall.
"Your either going to see a guy who looks old and tired versus a guy who looks young and fresh," Beckel said. "Or it will be [John] Edwards versus [Dick] Cheney where Edwards looked like a kid."
David Paul Kuhn and Avi Zenilman contributed to this story.
By Jonathan Martin