Anthony Constantino holds an 80% implied probability in the NY-21 Republican primary because of President Trump's endorsement and his positioning as the outsider business candidate in a district long represented by Elise Stefanik. Robert Smullen, a state assemblyman backed by the New York Republican Party and most county committees, trails at 21% as the establishment choice emphasizing legislative experience and general-election viability. Recent debates in late May highlighted sharp personal tensions between the candidates, including attacks on backgrounds and a post-debate handshake refusal, while Constantino's Trump support has consolidated primary voter preference ahead of the June 23 vote. Smullen's institutional advantages have not offset the endorsement effect in trader assessments of the closed primary outcome.