The primary is actually 31 separate contests, one in each of the state's state Senate districts, with anywhere from two to eight delegates divided between winner and loser.
That's where Bush, blacks and Hispanics come in.
The 126 primary delegates are distributed across the state based in part on the number of votes cast in the 2004 presidential and 2006 gubernatorial elections, rather than strictly on population.
State senate districts that gave Sen. John Kerry or the 2006 gubernatorial candidate, Chris Bell, a majority or even a sizable minority in their votes in 2004 and 2006 are favored with more delegates under the formula. That generally means areas that are home to blacks and liberals, in areas around Houston, Dallas and Austin, for example groups that have strongly favored Obama.
Election day polls in Texas from four years ago show blacks gave Kerry 83 percent of their votes in 2004, to 17 percent for Bush. Two years later, Bell claimed 63 percent black support in losing a four-way race to Republican Gov. Rick Perry.
By contrast, Kerry split the Hispanic votes with Bush, 50-49. Bell got less than that, 41 percent.
As a result, some state Senate districts with heavy Hispanic populations, including areas around Brownsville and Corpus Christi, have relatively few delegates at stake in this year's presidential primary.