Two transformations that changed patterns of party affiliation in modern Texas occurred at roughly the same time and are partly interdependent. One was the rise of the Republican Party in Texas. The other was federal enforcement of voting rights in all of the former confederate states. Many date the beginnings of a viable Republican Party in modern Texas to 1961 when an obscure college professor named John Tower won the U.S. Senate seat vacated by Lyndon B. Johnson, who became the Vice-President of the United States. (See Republicans Rising in the Political Parties chapter of Texas Politics.)
Just a few years later, after the passage of the federal Voting Rights Act of 1965, many of the official and extra-legal mechanisms used to exclude African Americans and other minorities from political participation were abolished or abandoned. The elimination of poll taxes and the introduction of federal oversight of redistricting helped to ensure minority access to voting and the chance for more ethnically and racially diverse choices once in the voting booth.
The Republican Party's ranks began to grow as the economic dynamism of the state attracted more and more Northerners with conservative and Republican orientations. Meanwhile, as more minorities began to participate, they gravitated toward the Democratic Party. In response, many conservative, white Texas Democrats switched horses, joining the newly competitive Republicans.
By the 1997-1998 term Republicans had won a majority of the seats in the state Senate, and after the 2002 election became the majority in the state House of Representatives as well. A graph of the number of seats held by each party in the Legislature since 1939 clearly illustrates the change in party power.