I am still a skeptic - especially for 2020 - but there is a very rapid change going on in Texas. First, the educated people in the suburbs are turned off by Trump. And second, Latinos - 40-45% of whom were reliable GOP voters in the Bush era - are apparently not happy about being called "invaders." I guess the GOP strategists just did not see that coming.
If this were to happen, and if it turned out to be sustainable, there would be no more GOP presidents in our lifetime. Might just be anti-Trump momentum...but the young people of Texas appear to be like young people everywhere - they are turning against the GOP in enormous numbers. Four GOP House members are retiring, which is certainly due to what their internal polling is telling them.
Lots of numbers here: https://www.cnn.com/2019/08/08/politics/could-texas-go-blue-2020/index.html
Link: https://www.politico.com/story/2019/08/12/texas-republicans-2020-elections-1456161