Pointing to a New York Times and Siena College poll published Sunday, Axelrod wrote on X, the platform formerly known as Twitter: "It's very late to change horses; a lot will happen in the next year that no one can predict & Biden's team says his resolve to run is firm."

Arguing Biden is "justly proud of his accomplishments," Axelrod said Biden's poll numbers will "send tremors of doubt" through the Democratic Party.

"Not 'bed-wetting,'" but legitimate concern, Axelrod wrote.

"Trump is a dangerous, unhinged demagogue whose brazen disdain for the rules, [norms], laws and institutions or democracy should be disqualifying," Axelrod wrote in a separate post. "But the stakes of miscalculation here are too dramatic to ignore."