Three days of disharmony between rival factions have been followed by three evenings of relative calm, unity and some fine speeches. In Philadelphia tonight, Hillary Clinton gets her turn. The oratory delivered by Michelle Obama, Bill Clinton and Barack Obama has helped her, but as acts to be followed they also make her task harder: Mrs Clinton is not a natural performer. In another era that would be a compliment; now a politician who can’t emote-on-demand is likely to be seen as inauthentic. Her themes will be security and creating an economy that works for more Americans. In an ordinary election cycle, these would be the wrong notes for a Democrat to hit after an eight-year Democratic presidency. But this one isn’t ordinary. Mrs Clinton needs to get the mixture of optimism and pessimism just right, co-opting the “morning-in-America” lines abandoned by Republicans while also acknowledging the country’s fears.