Kammala wannan jumla: Horowitz ya kasance babban dan wasa a Amurka a cikin shekarun 1930 da 1940. Ya kasance US Open Champion a 1936, 1938, da kuma 1943. A cikin 1941, ya rasa wasa (+ 0-3 = 13) tare da Samuel Reshevsky don Gasar Chess ta Amurka. Ya taka leda a tawagar Amurka a gasar Chess Olympiads hudu, a 1931, 1935,
A cikin sanannen wasan wasan kwaikwayo na Amurka da USSR a 1945, Horowitz ya zira kwallaye daya daga cikin nasara biyu kawai ga Amurka ta hanyar kayar da GM Salo Flohr. Ya raba "karamin wasan" na wasanni biyu da Flohr, kuma a cikin bugun 1946 na wannan taron, ya raba karamin wasan nasa da Isaac Boleslavsky.