One of the most sought-after presidential endorsements in a key early voting state is from a woman who cannot vote. As Democrats jockey for support in Nevada, a meeting with Astrid Silva, a 31-year-old immigrant rights activist who has become a public face of the “Dreamers,” is a can’t-miss early stop. Silva has had dinner with Kamala Harris, policy roundtables with Elizabeth Warren and Joe Biden, and vegan tamales with Cory Booker. Just this week, after Pete Buttigieg noticed she attended Supreme Court arguments on the program shielding her from deportation, the candidate called to make sure she knew he...