These charts are from the latest University of Texas / Texas Tribune Poll -- done between October 18th and 27th of 1,200 registered Texas voters. The poll has a margin of error of 2.83 points.
As the second chart shows, Trump is not very popular in Texas. Only 40% say they would definitely vote for him, while 46% say they would definitely vote against him. That shows some promise for Democrats.
But right now, the Democrats don't have a candidate that could beat Trump in Texas. Biden and Warren trail him by 7 points, and Sanders trails by 5 points. Castro trails by 13 points.
NOTE -- The poll was done before O'Rourke withdrew from the race, and had him trailing Trump by 6 points.
The survey also questioned Democratic voters, and the margin of error among them was 4.21 points. The result is shown below. Currently Biden leads with 23% and Warren is second with 18%.