Politics in the United States: Can non-resident aliens donate?

Federal Election Commission, oft abbreviated as FEC, regulations prohibit "contributions" from a few sources, foreign nationals being one of them.

Foreign nationals may not make contributions in connection with any election--Federal, State or local.

Please note that the term is "contributions" FEC clearly defines a contribution as

anything of value given to influence a Federal election is considered a contribution

As noted by James Green on meetup, volunteering might be an option for non-US residents. However, please remember to tread carefully as you might hurt your candidate/causes rather than helping them. If you have time, the FEC has many resources to guide you in this matter. The above quotes come from this brochure. However, there are many other pages that you could look up, including this brochure on volunteering. Before I end, I feel obligated to reproduce a footnote from the volunteering brochure:

The reader should not rely solely on this brochure but should also consult the Federal Election Campaign Act, Commission regulations and the referencedadvisory opinions.

Thank you for reading!