White independents have favored Obama in other states, though their support is unlikely to be monolithic for any one candidate in Texas, said Linda Curtis, founder and director of Independent Texans, an advocacy group that represents independent voters.
She noted that many of the state's independent voters are conservative by inclination, and could support home-state candidate Rep. Ron Paul, R-Texas, or former governor Mike Huckabee, R-Ark., who has made a broad populist appeal to voters.
"Obama's making a big play for independents, and they're very attracted to him," Curtis said. "But I don't think they're going to coalesce around any one candidate."
White Democrats in Texas are a fast-changing demographic group that look less like traditional Southern white voters every year, Frost said.
Younger white voters tend to be more liberal and clustered around the urban areas of Dallas, Houston, Austin, and San Antonio — and could support Obama, who has grown stronger among white voters as the campaign has progressed.
"The white vote in Texas has gotten more and more liberal as time goes on," Frost said. "Texas has never mattered up until now. … It's going to be close."
ABC News' David Chalian and Eloise Harper contributed reporting.