In just over a decade, Gabriel Attal has risen from a work experience recruit in the health ministry to the second-highest office of state in France. As of Tuesday, he has also become France’s youngest prime minister at 34 and the first openly gay leader of the government. It is a spectacular trajectory, even for someone from Attal’s privileged background, for whom each career advancement appears to have come remarkably easy. In the early years of Emmanuel Macron’s presidency, Attal was one of a group of well-educated young men from comfortable backgrounds picked to advise and support the equally young...