Editors at National Review Online urge former President Donald Trump to avoid the Kamala Harris “mistake.”

We hope that Donald Trump and his party are watching what is happening now with Joe Biden and Kamala Harris, and drawing the right lessons about choosing a running mate. The seriousness and consequences of that decision are now on full display.

The 81-year-old Biden’s age-related decline, which was laid bare before the world in Thursday’s debate, has provoked a series of crises. It is a political crisis for Biden, his campaign, and his party. It is a national-security crisis for a country whose commander in chief is plainly not up to the full-time job of the presidency, especially outside the hours of 10 a.m. and 4 p.m. on weekdays. And it threatens to become a constitutional crisis if Harris and Biden’s cabinet need to contemplate invoking the 25th Amendment over Biden’s objections.

At every turn, the presence of Harris in the second-highest office exacerbates the crises. Biden’s party could coalesce around a movement to pressure him to step aside — but Harris is so unpopular and so plainly unsuited to the presidency that Democrats blanch at putting their fate in her hands. Voters could more easily accept a caretaker figurehead as president if they had confidence that a trustworthy No. 2 was increasingly running things and ready to step in at a moment’s notice. Instead, Harris has hemorrhaged staff, become a figure of mirth for the rambling platitudes of her public remarks, and found herself conspicuously assigned only tasks that were already doomed to failure. Nobody in this administration treats her as if they respect her.

Worse, because Harris was chosen in large part for her demographic profile as a black woman — certainly not for her accomplishments, her political success, or her talents, none of which recommend her for any serious job — it is politically painful for Democrats either to replace her on the ticket or pass her over if they replace Biden. Live by identity politics, die by it slowly.