Nonetheless, Ms. Ocasio-Cortez, a 28-year-old community organizer who has never held political office, is trying to leverage her fame to promote other progressive candidates — many female, and almost all viewed, as Ms. Ocasio-Cortez was, as long shots. She has waded into races on the federal, statewide and local levels, with the same message: The time for discounting female and outsider candidates has passed.