Trump Steps Up, Helping Biden Just When the President Needs Him

If anyone gets a thank-you note from President Biden for helping get him out of a jam in recent days, it should probably be former President Donald J. Trump.

Just when Mr. Biden was swamped by unwelcome questions about his age, his predecessor and challenger stepped in, rescuing him with an ill-timed diatribe vowing to “encourage” Russia to attack NATO allies that do not spend enough on their militaries.

The stunner from Mr. Trump over the weekend not only drew attention away from the president’s memory problems, as detailed in a special counsel report, but also provided a convenient way for Mr. Biden’s defenders to reframe the issue: Yes, they could now say, the incumbent may be an old man who sometimes forgets things, but his challenger is both aging and dangerously reckless.

It was not the first time, nor likely will it be the last, that Mr. Trump has stepped up when an adversary was in trouble to provide an escape route with an ill-considered howler of his own. Mr. Trump’s lifelong appetite for attention has often collided with his evident best interest. For Mr. Biden, that may be the key to this year’s campaign, banking on his opponent’s inability to stay silent at critical moments and hoping that he keeps reminding voters why they rejected him in 2020.

“There’s a saying that the enemy of your enemy is your friend,” said Alex Conant, a Republican strategist who worked on the 2016 presidential campaign of Senator Marco Rubio of Florida, who lost the party nomination that year to Mr. Trump. “Since Trump is his own worst enemy, he’s arguably Biden’s best friend.”

That does not mean that age is no longer a political liability for Mr. Biden, who at 81 is already the oldest president in American history and would be 86 at the