Politico has this important article on this 1996 law review article co-authored by Judge Sotomayor. The material discussed in the article is the text accompanying notes 28-30 and 58-60.
As I stressed to the Politico reporter, the article makes clear that as a matter of policy, the judge believes reasonable campaign finance regulation serves important anti-corruption and other interests. But that does not necessarily tell us how the judge would rule as a Justice on the Supreme Court facing campaign finance statutes challenged under the First Amendment. A better way to judge that (though still not perfect, because lower court judges feel more bound to follow existing Supreme Court precedent than sitting members of the Supreme Court do) is to look at how the judge has ruled in election law cases.