If you were to try to guess the political affiliation of a Texas legislator and had nothing to go on other than race, you would still get the right answer most of the time. Most of the black and Hispanic legislators are Democrats. Most of the white legislators are Republicans. There are some exceptions, but the lines are fairly sharp.

Voters decided which candidates should go to Austin, but the political mapmakers there decided which voters would be deciding which races. Starting with the political districts drawn more than a decade ago by Texas Republicans — led by Tom DeLay, R-Sugar Land, then the United States House majority leader — white Democratic officeholders became increasingly obsolete in Texas.

DeLay’s concern had to do with a pack of entrenched Democrats in the state’s congressional delegation. Their distinguishing feature, for his purposes, was their party affiliation. He and the legislators working with him successfully used the state’s changing political characteristics and its changing demographics to take those Democratic veterans out.

What had once been a swing state had become, by then, a Republican one; DeLay and his allies argued that a state where well over half of the voters were choosing Republicans in statewide elections should display similar proportions of Republicans in Congress. The mapmakers were also required to make sure any new political maps properly reflected the growth of minorities in the population.

“Texas Anglos vote about 70 percent Republican, while Texas Hispanics vote about two-thirds Democrat, and Texas blacks vote 90-plus percent Democrat,” said Cal Jillson, a political science professor at Southern Methodist University.

Given that data and the requirement to protect growing numbers of minority voters, the maps drawn in 2003 squeezed out the incumbent white Democrats targeted by the Republicans. Minority Democrats were protected. Whites were not.

“As fewer and fewer Anglos vote Democratic, and the number of minority-majority districts rises, the native habitat of the Anglo Democrat has shrunk considerably,” said Mark P. Jones, chairman of the political science department at Rice University. “Thus there are simply less races for Anglo Democrats to run in where the party has a ghost of a chance of victory.”

The demographic changes were even stronger when the 2010 census came out and the next round of redistricting started. Democrats were not any stronger in statewide races in Texas, but they had made significant inroads in legislative races during the decade. That census year, of course, was also the year Republican and Tea Party voters forcefully asserted themselves. In Texas, they voted out one-third of the Democrats in the Legislature and installed a supermajority.

Their timing was perfect. That was the Legislature charged with the next round of redistricting, and lawmakers baked their big Republican majority into the maps that would be used for the next 10 years.

Republicans lost a couple of seats in 2012, but even the most ardent conservatives expected that to happen. They still have 95 members of the 150-member House and 19 members in the 31-member Senate. A few seats could change hands in this year’s general election, but existing Republican advantages should hold.

Changes in the ethnic and racial makeup of the Legislature continue. Two of the remaining white Democrats in the House — Lon Burnam of Fort Worth and Craig Eiland of Galveston — are leaving. Burnam lost his primary to Ramon Romero Jr., and Eiland declined to seek re-election. He will be replaced by either Wayne Faircloth, a Republican, or Susan Criss, a Democrat, in one of the few swing districts left. Earlier this year, state Rep, Mark Strama, Democrat of Austin, resigned and was replaced in a special election by Celia Israel, also a Democrat.

Seven white Democrats remain in the House alongside seven minority Republicans, the exceptions to the prevailing parallel between party and race in that chamber. The Senate’s 19 Republicans are Anglos, and nine of 12 Democrats are black or Hispanic. The congressional delegation includes two Anglo Democrats and one Hispanic Republican — Senator Ted Cruz.

Disclosure: Rice University is a corporate sponsor of The Texas Tribune, and Southern Methodist University was a corporate sponsor in 2013. A complete list of Texas Tribune donors and sponsors can be viewed here.