The race in Texas is tight, with Clinton and Obama essentially tied, at 50-48 percent, according to the latest CNN/Opinion Research Corp. poll.
Both candidates face off against one another in a debate Thursday in Austin, Texas, the last before voters go to the polls in Ohio, where 141 delegates are at stake, and Texas, which has 193 delegates.
The Clinton campaign has suggested the way Texas proportions its delegates may unfairly punish Clinton, who has targeted Hispanic areas that yield fewer delegates.
Ohio and Texas are now must-wins for Clinton's presidential candidacy, where she will spend the next two weeks trying to stop the undeniable momentum Obama has going into the delegate-rich contests on March 4.
"It's not going to be enough for her to win now in Texas and Ohio," ABC News' George Stephanopoulos said on Wednesday's "Good Morning America."
"In order to catch up in the delegates now she's going to have to beat him by the kind of landslides he's been beating her by."
ABC News' Gary Langer, Kate Snow, Sunlen Miller, Eloise Harper, Bret Hovell, Ron Claiborne, Teddy Davis and Kevin Chupka contributed to this report.