The 20th is a heavily Democratic district; it has not supported a Republican for president since 1956. In 1972, this was one of two congressional districts in the state of Texas to vote for George McGovern (the other being the 18th District in Houston). In 1984, this district gave Walter Mondale 59% of its vote.
Democratic challenger Joaquín Castro defeated Republican challenger David Rosa in the race for Texas's 20th district on November 6, 2012.  Prior to being elected, Castro served as a state representative of the Texas House from the state's 125th District.