Does a trip to Puerto Rico count as a trip outside the United States for the purpose of N-400 (Application for Naturalization)?

Question

I wonder whether a trip to Puerto Rico (PR) count as a trip outside the United States for the purpose of N-400 (Application for Naturalization). I'm looking for an official source.

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Details:

I found https://www.avvo.com/legal-answers/does-a-trip-to-puerto-rico-count-as-a-trip-outside-2188289.html:

No, a trip (and stay) in PR does not count, since PR is US Territory, and as such your trip to PR was the same as domestic travel to any one of the 50 states.

However, this is incorrect: some US Territories do count as a trip outside the United States for the purpose of N-400. E.g., from https://www.uscis.gov/policy-manual/volume-12-part-d-chapter-4:

USCIS will only count residence in the Commonwealth of the Northern Mariana Islands on or after November 28, 2009, as time counted for physical presence within the United States for naturalization purposes.

And the Commonwealth of the Northern Mariana Islands [became a US territory in 1975](https://www.doi.gov/oia/islands/cnmi#:~:text=The%20Federal%20law%20(the%20Covenant,and%20immigration%20law%20in%202008.):

The Federal law (the Covenant) making the CNMI a U.S. territory passed in 1975.

which means between 1975 and 2009, the Commonwealth of the Northern Mariana Islands was a U.S. territory but counted as a trip outside the United States for the purpose of N-400.

Answer 1

A trip to Puerto Rico does not count as a trip outside the United States for the purpose of N-400, since according to INA 101(a)(38), the term "United States" includes Puerto Rico (emphasis is mine):

From Title 8-ALIENS AND NATIONALITY CHAPTER 12-IMMIGRATION AND NATIONALITY SUBCHAPTER I-GENERAL PROVISIONS

[...]

8 USC 1101: Definitions

[...]

(36) The term "State" includes the District of Columbia, Puerto Rico, Guam, the Virgin Islands of the United States, and the Commonwealth of the Northern Mariana Islands.

[...]

(38) The term "United States", except as otherwise specifically herein provided, when used in a geographical sense, means the continental United States, Alaska, Hawaii, Puerto Rico, Guam, the Virgin Islands of the United States, and the Commonwealth of the Northern Mariana Islands.