“He has been durable,” said David Axelrod, a longtime political strategist for President Barack Obama. “The question is whether that durability is because we aren’t fully geared into the race or whether there are inherent strengths there.”…

The attacks from Harris and others have also prompted Biden advisers to encourage the former vice president to step up his campaign activities, including more question-and-answer sessions with voters and reporters, an approach that has been on display during his four-day Iowa swing. But that comes with risk for a freewheeling politician with a history of verbal fumbles…

Biden’s ultimate success in the race will depend in part on whether voters’ warm feelings toward him will help excuse his frequent missteps or see them as a sign that the candidate — who would be the oldest president ever elected — has lost a step.

“He’s always been prone to gaffes. That was true when he was in his 40s, 50s and 60s,” Axelrod said. “The difference is because people are looking for signs of potential deterioration, gaffes that would be written off as Joe being Joe can become much more damaging to him.”