In the 1996 presidential election, the age of Sen. Robert Dole, who at 73 was the oldest man ever to run for the office, was a substantive issue. Although he was thought to be in good general health, his right kidney had been removed, his remaining left kidney had stones, his electrocardiograms in 1980 and 1981 were abnormal, he had pre-cancerous colonic polyps removed in 1985, and he had undergone a radical prostatectomy for cancer in 1991.

He had smoked for many years and had a family history of heart disease, aneurysm, emphysema and cancer. In 2004, which would have been the last year of a second term if he had won, he had hip replacement surgery followed by a brain hemorrhage.

After the election, Richard Brody, a political scientist at Stanford, and I, in an extensive study of the media coverage at the time (published in 1998 in the Political Science Quarterly,) found that allusions to Dole's age were common, but with only occasional comments on its potential consequences. The impact of aging and ill health on the cognitive capacities essential for an effective presidency was poorly conveyed to the American public.

Hence, more than 60 percent of respondents to surveys were not concerned about Dole's age. Among those for whom age was an important consideration, four times as many voters believed that Dole's age would hamper him as president. That group of the electorate was far more likely to vote for Clinton.

The issue of age is with us once more with Senator John McCain's run for the office. James Reston, the great New York Times journalist of the last century, believed that younger presidents might be more resistant to the stresses of the job. "It is not responsible in this violent age to pick candidates for the presidency from men in their 60s," he wrote.

How would he have reacted to a president who would be 72 at his inauguration and 80 years old in the last year of a second term? The question is a fair one because McCain, if elected, would be the oldest person to be inaugurated in our history. While the Constitution endorsed age discrimination by setting 35 years as the youngest age of a president, it established no upper age limit, perhaps because life expectancy was so much shorter in 1787 than in 2008. When we choose presidents 65 or older, we must grapple with the possibility that they may be unable to fulfill the 208-week-long contractual obligation implicit in their candidacy.

Dominating the illnesses that affect the elderly are heart disease, stroke, cancer, infection, hip fractures, the complications of major surgery and dementia. Heart attacks are frequently accompanied by anxiety, depression, impaired concentration and problems with sleep. Following a stroke, depression, anxiety and emotional lability characterize many patients. A major sequel of surgery is confusion severe enough to impede one's ability to think clearly. The many drugs that the elderly use have significant side effects and may produce cognitive changes.

Dole and McCain supporters may respond, "Why worry about it when the institutional constraints guard us from irrational behavior in the White House?" Because the inherent risks are too great. As Sen. McCain said in a recent interview, "I understand that my age would be a factor at any time."

The term "cognition" refers to the interaction of mental processes that produce human thought. Under its rubric come such faculties as concentration, attention, inventiveness, intuition, memory, foresight, abstract and logical thought. All are applicable to meaningful decision-making, and many are essential when time is short and tensions high. The elderly are more sluggish at processing and retrieving information from short- and long-term memory. There is a 60 percent slowing in the rate of memory search between the ages of 20 and 50 years.

To be sure, both the health problems and the memory changes are unevenly distributed among the population. But why take a chance? Why push the odds and run for the most demanding job in the western hemisphere at an age when illness abounds, memory suffers and energy flags? This is the period when the elderly need their afternoon nap and the absent-minded become more so.

Clearly, some great leaders have functioned well beyond the age of 70. But the presidency is a position that is uniquely and awesomely demanding, extending well beyond thoughtful, meditative policy decisions. It includes many large and pressing operational components, interacting with the White House staff, the cabinet, the Congress, the media, the public, the international community and many elements within the political party system. It is a stressful, power-packed, exhausting job, requiring stamina and energy during long days, weeks and months. It may involve rapid responses to emergencies and crises, with decisions based on a level of accelerated information retrieval and processing that elderly presidents may lack.

Those for whom Dole's age was important and who voted for Clinton in 1996 understood the increased likelihood of illness: in comparison to men aged 45 to 54 years, those aged 75 to 84 years are 34 times more likely to die of stroke, 17 times more likely to die of heart disease, and 12 times more likely to die of malignancy. Nineteen percent of those between 75 and 84 years and almost half over 85 are affected with Alzheimer's disease. While older Americans might have thought that an older person such as Dole would best represent their interests, they were also profoundly aware of their own fragility as they moved along in their seventies.

The media have an obligation to the public. If age affects the quality and duration of a president's performance, as it does, the national interest is best served by making certain that the public is well informed. Thus far, attention to McCain's age has focused on the importance of his choice for vice president. By this time, the media should have demanded and obtained the most recent medical data from McCain.

Dole made public his medical record in detail when he ran. McCain did so in 1999, but has not released the results of a recent comprehensive examination. The voters deserve no less from him, from Clinton, and from Obama. Certainly McCain will want his physicians to inform the voters on the status of his malignant melanomas, diagnosed on four occasions, one more serious than the others.

The Congress also has an obligation. An upper limit on the age of candidates could be achieved by passing a Congressional resolution. This would represent a powerful deterrent to seniors who wish to run and to politicians who would like to nominate them, while leaving the Constitution intact. Madison and Hamilton, who understood the wisdom of a lower limit 200 years ago (when emergency decisions were rarely required) would appreciate the deference to the radically different, complex, interconnected world that we live in today.

An upper limit of 60 to 65 would recognize that the presidency is too demanding - physically, intellectually, psychologically, and emotionally - to place the burden on the shoulders of a senior citizen.

Herbert L. Abrams is a professor at Stanford University School of Medicine and a member-in-residence of the Stanford Center for International Security and Cooperation. He is the author of "The President Has Been Shot: Disability, Confusion and the 25th Amendment" (1992, WW Norton Inc.) and has written about presidential disability and its impact on decision-making.