If Texas is within 2% on election day, then we can talk about it being a realistic target for dems in 2020. If not, accept its relative closeness as a consequence of a literal fascist being the republican nominee, expect it to revert back to 57-43 R (TPV) in 2020, and check back in 15 years. Under no circumstance do I actually see TX voting for Clinton.
No, Hillary Clinton has to win Texas for it to be a legitimate chance for her or her Democratic successor (reasons of health?) to win it in 2020. The state still leans clearly R, and will revert to "safe R" in 2020 with some Republican other than Trump as the Presidential nominee. Obviously she will much more likely win the Presidency without Texas than with it. She has to win about 400 other electoral votes to have a real chance to win Texas.
It is not Hillary Clinton who would win Texas; it would be Donald Trump who loses it. Donald Trump has offended enough sensibilities that he could lose Texas.
Texas can go Democratic, but such suggests that America is undergoing an era of Democratic dominance as with the Second New deal.