Originally Posted by
Aussienarelle
Would not have occurred to me to take my passport with me to a US territory.
Strictly speaking, as a matter of law, foreigners are required to carry proof of legal presence at all times:
https://www.uscis.gov/ilink/docView/...-0-0-8289.html
I haven't flown to/from P.R. in a long time, but I'm guessing ICE pays closer attention to those flights, since it's not uncommon for people to enter P.R. illegally.