I have a hard time seeing Texas go Democratic before Iowa and ME-02.
Actually I think Texas is more vulnerable than Iowa largely due to demographics. It is far more urban and generally urban areas are much more likely to oppose Trump than rural. Also Texas is a minority-majority state while Iowa is one of the few that is still over 90% white and despite Trump's low approval rating I still expect he will win the white vote in 2020 (note Lyndon Johnson is the only Democrat post WWII to win the white vote and likewise Romney won the white vote by 20 points, McCain by 12 and both still lost handidly). I think in the future you will increasingly see it go along racial lines with the more racially mixed areas going Democrat and the whiter areas going Republican.
