Tonight on The Last Word: Vice President Kamala Harris and Gov. Tim Walz push a hopeful message in their first joint rally. Also, Speaker Emerita Nancy Pelosi discusses her new memoir, “The Art of Power: My Story as America’s First Woman Speaker of the House.” And the “March For Our Lives” gun safety group backs the Harris-Walz ticket. Rep. Joanna McClinton, Sen. Tina Smith, Speaker Emerita Nancy Pelosi, and David Hogg join Lawrence O’Donnell.