Amid the public fretting and finger-pointing rage over how to deal with a Democratic presidential nominee who most Americans think is too old for the job, some of the frustration is being directed at the first lady, Jill Biden. Which has me thinking back to one of the viral moments from her husband’s 2020 campaign.

On the night of Super Tuesday, as Joe Biden was delivering his celebratory speech at a rally in Los Angeles, two anti-dairy demonstrators rushed the stage, only to run smack up against the protective wall of Dr. Biden. With impressively fleet feet — rocking metallic sling-back pumps, no less — she inserted herself between her man and potential harm. There is an amazing photo of her grimacing and holding a protester at bay by the wrists as Mr. Biden looks on with concern. “We’re OK,” she assured everyone once the spectacle was over. “We’re OK.”

Notably, this was not the first time the candidate’s wife had served as a human shield for him in that race. Less than a month earlier, on the eve of the New Hampshire primary, she blocked an aggressive heckler and then showed him the door, joking afterward, “I’m a good Philly girl.”

Philly tough. That is who Dr. Biden is, fiercely and reflexively, when it comes to protecting and supporting her husband. This has been her role since the couple’s courting days, when he was a young senator struggling to recover from losing his first wife and baby daughter in a car crash. And those looking to recruit her to encourage Mr. Biden to reconsider his presidential bid may sorely misunderstand her — and their marriage.

“She gave me back my life,” he gushed of Dr. Biden in his 2007 memoir, “Promises to Keep.” Even before officially joining the family, she became a surrogate mother to his two young sons. And for nearly half a century since, she has sustained her husband through enough high-intensity drama to shatter a lesser spouse: his near-fatal aneurysm, the death of his oldest child, the disastrous drug addiction of his younger son, multiple presidential runs.

Which means that if Mr. Biden is determined to stay in this race, Jilly, as he calls her, is going to have his back. Period. Even if much of his own party suspects that he is very much not OK. In fact, the more that elite establishment types clamor for him to move aside, the more Dr. Biden is likely to get her back up.