If you need a passport super short notice (possibly same-day) you can go to one of a few passport offices and hope they can fit you in. I looked into it a few years ago when I lost my passport right before a big business trip. Logistically it wouldn’t have worked for me (by the time I even got to the Boston office on that Monday my flight would have left), but yeah. Found my passport a few days later, tucked into a notebook.