Final answer:
The key issue for nativists regarding Hispanics is immigration, specifically illegal immigration and its perceived impact on American culture and resources.
Step-by-step explanation:
The main "hot button" issue that triggers nativists' ire more than any other ethnic manifestation by Hispanics is immigration, specifically illegal immigration from Latin America to the United States. Nativists, who prioritize long-established American citizens over newcomers, often express concerns about the country's culture, resources, and security being compromised by immigrants.
Intense debates and controversial policies have revolved around immigration reform, such as the DREAM Act, border security measures like the proposed wall, and state-level legislation like Arizona's SB 1070, which have all sought to address various aspects of this issue.