evidence: A new presidential candidate, a slew of celebrities and slick programming helped propel Democrats and Vice President Kamala Harris to a ratings win at this week’s Democratic National Convention, surpassing the television viewership of last month’s Republican gathering. [...] Excitement over her candidacy — as well as high-profile speeches by former President Barack Obama, former Secretary of State Hillary Clinton, and former first lady Michelle Obama — helped fuel viewership. So did appearances by a host of celebrities, including Stevie Wonder, John Legend, Pink, Kerry Washington and Mindy Kaling.