On the eve of the first indictment, the night before the former president flew to Manhattan to be fingerprinted and arraigned, Donald Trump’s pollster told RealClearPolitics a paradox: Historic legal trouble would “really help us in the primary.” At least, the pollster added, “in the short term.” Allies of Ron DeSantis expected as much. Top officials with a group supporting the Florida governor’s campaign, a super PAC called Never Back Down, started a real-time experiment to quantify the fallout from the indictment while testing their ability to conserve DeSantis’ support, maintain his positive image, and reach new voters. Among those...