Days before a special counsel’s report put President Biden’s advanced age in the spotlight, the Wall Street Journal asked Vice President Kamala Harris about what it calls a “delicate question” for the campaign: Whether she has to convince voters that she is “ready to serve” as president. “I am ready to serve. There’s no question about that,” she replied, adding that everyone who sees her on the job “walks away fully aware of my capacity to lead.” Biden, 81, is already the oldest president in US history and would be 86 by the end of a second term. Harris, 59, and other Democrats have pushed bac…