FWIW, not just naturalized citizens, if you expand the 'Foreign Nationals' entry under 'Who can't contribute' in [0] it expands to:

An individual who is not a citizen of the United States or a national of the United States and has not been lawfully admitted to the U.S. for permanent residence, as defined in 8 U.S.C. § 1101(a)(20); or ...

Suggesting that you can also donate if you have permanent resident status (aka 'green card holder'), regardless of citizenship.

[0] https://www.fec.gov/help-candidates-and-committees/candidate...