Anti-Irish sentiment in the United States previously involved depictions of Irish migrants as non-human primates. While historians have debated the prevalence of contemporaneous "No Irish Need Apply" signs, such a sentiment was widely discussed, with Irish Americans referencing it after 1860. For the sake of this question, I take the decline in both of these phenomena as suggestive of a decline in US anti-Irish sentiment.
Sources such as Ignatiev 1995 argue Irish migrants to the United States were initially perceived as non-white, and that the subsequent classification of Irish Americans as white and the decline in anti-Irish sentiment was largely driven by Irish alignment with anti-black racism, beginning with support for the Democratic Party in the antebellum North. The idea that Irish Americans have only recently been considered white is often cited, at least by non-historians, as an example of how whiteness is a social construct.
However, Arnesen 2001 argues such analyses conflate race with economic status and ignore the legal rights provisioned to Irish immigrants c. 1830, and concludes a former classification of Irish people as not white is a product of historical revisionism.
Is a changing definition of whiteness part of the explanation for anti-Irish sentiment's decline in the US? Is anti-black racism among Irish Americans part of the explanation for said decline or such a change in definition? What other factors were integral to the decline in anti-Irish sentiment?