Bobby Kennedy Jr. is the first environmental activist with a legitimate shot at winning a major-party nomination for President. He has made preserving and cleaning up the environment his life’s work, rescuing the Hudson River from polluters and turning it into the centerpiece of the country’s healthiest watershed and winning billions of dollars in fines from corporate polluters in hundreds of lawsuits that have served as a powerful counterweight to avarice and greed. Kennedy’s emergence this summer as a dark-horse challenger to Biden only surprised people who make a habit of not paying attention. To them, Kennedy was a marginal weirdo and probably a nut, an aging Prince Hal who had disqualified himself from serious politics by tilting at too many windmills to count. Most recently, Kennedy had made a name for himself as an “anti-vaxxer,” a designation that signifies a worrying inclination to question large pharmaceutical companies about the safety of their products.  The meteoric rise …