There is no way to watch Biden's Hanoi press conference and not recognize that his brain is working fine. He responds to questions in appropriate fashion. His words are diplomatically chosen, and his thoughts follow in logical order.

Anyone who has ever had a friend or relative with dementia knows that this is nothing like what they sound like. They repeat themselves constantly without self-awareness. They don't distinguish between things that happened that morning and things that happened years ago. They get angry and tearful for no apparent reason. Dementia is a devastating disease and quite different from normal aging. In fact, while the percentage of people with dementia rises with age, only about 10% of those aged 70 and older suffer from it.

Now, have a look at Biden's press conference. He was asked about a Chinese official's accusation that Biden was "insincere" about the relationship with China, and also whether he thought Chinese President Xi Jinping was sincere in light of his recent move to "ban" Apple in China. Biden had trouble hearing the first part of the question (OK, that is his age showing), but then gave a careful answer.

He declined the implied invitation to get into a spitting match with Xi and emphasized that "we're not looking to hurt China ... We're all better off if China does well," adding that "if China does well by the international rules, it grows the (world's) economy." To underline that point, he noted that "It's not about isolating China. It's about making sure the rules of the road — everything from airspace and — and space and in the ocean is — the international rules of the road are ... abided by."

Without overt threats or intemperate words, Biden then noted that he is building and/or bolstering alliances with other Asian nations. "That's what this trip was all about: having India cooperate much more with the United States, be closer with the United States, Vietnam being closer with the United States. It's not about containing China; it's about having a stable base — a stable base in the Indo-Pacific."

I could have done without the too-clever-by-half tactic of calling only upon female journalists (a reprise of an Obama gimmick from 2014). And Biden's acknowledgement at the start that the five questioners had been chosen in advance was a mistake. He introduced the Q and A by saying, "And now, I will take your questions. Let me see. They told me — they gave me five people here," which made him seem directed by others instead of in charge. And he stumbled over their names all the same.

But in the course of his basically direct, non-meandering answers, he touted the new rail and shipping corridor just announced at the G20 that will link India to Europe; noted that the United States has the world's strongest economy; praised a past Republican senator for working with poorer nations to maintain forest land; and mentioned the amount of carbon the Amazon rainforest absorbs.

At one point he did sound like a geezer, quoting from a John Wayne movie, but that was one deviation from an otherwise workmanlike performance.

Biden's physical presentation — the slow and careful walk, the slightly pitched posture — suggests age more than his words. But, bottom line: He is perfectly capable of thinking on his feet. Too many Americans have come to believe that he is in sharp mental decline. When you see him in a Q and A, it's clear that he isn't, and people need to know that.

Mona Charen is policy editor of The Bulwark and host of the "Beg to Differ" podcast. Her new book, Hard Right: The GOP's Drift Toward Extremism, is available now.