Perception is king in power politics. Audiences foreign and domestic take the measure of the leadership of a powerful nation—a behemoth like the United States. How observers gauge the capability, competence, and fortitude of that nation’s leadership determines how seriously they take statements of purpose issuing from its capital. If they hold a president in slight regard, they will take his or her words lightly—and shape their actions accordingly. Aggressors will be emboldened. They will be neither deterred from aggression nor coerced into actions they resist taking. Foreign allies, partners, and friends will blanch. The superpower’s commitments to them will lose credence.

Foe and friend alike will look to their own devices to advance their interests and purposes. As they turn away the superpower’s international standing and claim to leadership will decay.

Now, human perception is fickle. Perceptions of a leader’s mental keenness may be neither accurate nor fair. They matter all the same. They sway what other governments, societies, and armed forces do. That augurs ill for American stewardship of the liberal world order, a system the nation has presided over since defeating imperial Japan in 1945.

I refer, of course, to last Thursday’s presidential debate between candidates Joe Biden and Donald Trump. In the debate’s aftermath voices from across the political continuum adjudged President Biden’s performance proof of mental infirmity. The New York Times editorial board clamored for Biden to quit the race for the good of the country. Veteran Washington Post journalist Bob Woodward pronounced the president’s showing “so bad, so awful” that it dumped a “political hydrogen bomb” on the White House.

Nor were the alarm—or jeers—confined to North America. The Wall Street Journal canvassed European political leaders and opinionmakers for their views. Nathalie Tocci, director of the Institute of International Affairs in Rome, reported that “The reading in Europe is that this has been an unmitigated........

© The National Interest