Originally Posted by
MSPeconomist
I agree. If the OP lives anywhere near a USA passport agency, go there ASAP with your documentation, including copies of plane ticket receipts, hotel reservation confirmations as well as proof that the kid is a USA citizen; you'll probably need both parents. The passport agencies are great at processing passports in a day or less, although my experience is only with renewals.
It's best to make an appointment but I've observed "no appointment" lines/windows that do indeed process those without appointments even though the official information says that appointments are required. Going without an appointment just means that you're likely to wait longer.
OP will need to get a USA passport for the baby anyway, and hoping the expedited route through a USA passport agency is the most efficient way to do this, so rather than cancelling the trip, view it as a convenient apportunity to process the kid's passport quickly and efficiently.
WIth a US state birth certificate, both parents present along with their own passports, the child, and a properly completed passport application with appropriate photos and proof of imminent travel, a same-day passport is possible at various US passport agency offices on Monday. But today they are usually closed. For most of the agency offices, I would just show up with or without an appointment.