The joyful reception that Vice President Kamala Harris received from Democrats when President Joe Biden dropped out of the race and endorsed her was rooted largely in the contrast between the relatively youthful 59-year-old woman and the increasingly frail 81-year-old president. She gives good speeches! She's fun and energetic! And she can campaign aggressively, especially with Biden remaining president, allowing Harris to make campaigning her full-time job. People in focus groups frequently say they haven't seen much of Harris these past four years. Well, that's about to change, since she is well-positioned to give endless interviews, attend frequent events, and give oh-so-many speeches. The contrast with Biden, who struggled to find the energy to campaign on top of running a country, will be notable. 

Every time Trump talks, it confirms the Biden campaign's narrative that the former president is a self-centered jerk who will sell out the country for his own interests.   

Amanda Marcotte  in Salon.com