When Pope Benedict XVI announced that he would abdicate the papacy, he explained that "in today's world, subject to so many rapid changes...both strength of mind and body are necessary, strength which in the last few months, has deteriorated in me to the extent that I have had to recognize my incapacity to adequately fulfill the ministry entrusted to me." By becoming the first pope to resign since the 15th century, Benedict demonstrated a self-knowledge that is incredibly rare among leaders. Contrast his behavior, for example, with that of New Jersey Senator Frank Lautenberg, who before being forced to stand aside described Newark Mayor Cory Booker as a "disrespectful" child for challenging his reelection bid, even though Lautenberg would have been almost 92 when he was sworn in.
It may be a fraught subject, but aging often has enormous effects on people's personalities and cognitive function. Some leaders can maintain their vitality and abilities into extreme old age, but after enough time in office, a leader's performance probably will decline, perhaps precipitously. And, although many scholars argue that leaders have little impact on foreign policy because political systems tend to produce dispensable candidates, there are specific circumstances in which individuals become enormously important -- one of the most notable being when they change radically once in office, surprising the system. This is precisely what happens to anyone who spends a long time in senior government positions, because of both the effects of power itself on those who wield it, and the effects of age on every human being.
Power itself has profound, and usually toxic, effects on those who have it. CEOs are so pampered that comparing them to babies is surprisingly illuminating (and very funny). What is true for a CEO is, in this case, even more true for the men and women who lead nations and can literally have power over life and death. Over time this authority is likely to have profound effects on most people's personalities. It would be remarkable indeed for any person treated with deference and pampering for years, even decades, to not be affected by it. Even worse, power tends to make those who have it more sociopathic. They become more impulsive, more Machiavellian, and more willing to dehumanize those who lack it. What's more, leaders are almost invariably surrounded by family and staff who depend on them for continued access to the perquisites of power, and so often hide evidence of erratic behavior or decline. Woodrow Wilson's wife Edith hid his crippling stroke, Nixon's senior staff conspired to conceal his alcoholism, and Anthony Eden's doctor helped cover up his illness and addiction to amphetamines during the Suez Crisis.
The effect of age is equally worrying. Aging can have a powerful and largely negative impact on leaders in three ways. It can greatly increase their vulnerability to illness, shift their personality, and decrease their cognitive abilities.
It is a sad fact of life that the passage of time depletes the energy of every person and renders all of us more vulnerable to illness. Physical ailments can have surprisingly powerful effects on decision-making. As Roy Baumeister and Jon Tierney describe in their book, willpower is depleted by conditions as seemingly minor as the common cold, making it considerably more difficult to delay gratification or make difficult decisions, because the cold depletes the blood glucose critical for brain function. Driving when you have a severe cold, for example, is statistically more dangerous than driving while mildly intoxicated. More broadly, in Presidential Leadership, Illness, and Decision Making, Rose McDermott described how illness can make leaders unpredictable, limit their attention spans, shorten their time horizons, and diminish their cognitive capacities. Wilson's stroke, for example, intensified his natural rigidity and eliminated any last hopes of American entry into the League of Nations. In The Impact of Illness on World Leaders, Bert Park, a neurosurgeon, makes a powerful case that age-related dementia in Paul von Hindenburg was a key factor enabling Hitler's rise to power. Hindenburg was 82 when he defeated Hitler to win re-election to the presidency of the Weimar Republic in 1932. He twice rejected any role for Hitler in the government, until, at the age of 84, his increasing weakness led to his tragic agreement in January 1933 to make Hitler chancellor of a government otherwise staffed by non-Nazis.
Even beyond the immediate effects of illness, aging can have pronounced effects on personality. Put simply, in general people really don't mellow with age. Instead, Jerrold Post and Bert Park have shown that they tend to become exaggerated versions -- almost caricatures -- of themselves, with their normal tendencies and patterns becoming intensified. This tendency is particularly likely to affect foreign policy. The aggressive can become belligerent, the passive, apathetic. Tendencies that would otherwise have fallen within an acceptable range can suddenly become problematic -- a shift that, when it happens to a head of government, is particularly likely to upset foreign policy.