Horacio Daniel Usandizaga (born June 15, 1940 in J.B.Molina, province of Santa Fe, Argentina), also known informally as El Vasco (Spanish: The Basque), is an Argentine politician.
A man of hot temper, Usandizaga had publicly promised that he would leave if Carlos Menem was elected president, as eventually happened.
Usandizaga stood as candidate for Governor of Santa Fe in 1991, 1995 and 1999, but on all three occasions he failed to win, in part due to the electoral system in place at the time (the now-repealed Ley de Lemas).
He was elected as the provincial representative (Diputado) in the National Congress in 1993, and was a member of the Argentine Senate from 29 November 1995 to 9 December 2001.
He was re-elected, but at the end of 2002 he announced he would retire from active politics upon the partial renewal of the Upper House on 9 December 2003.