I live in Florida in the heart of Trump country. Sucks don't it? But there are other parts of Texas(and Florida) which are not so much in favor of Trump.

Trump won by 9% in Texas against Clinton.
Beto lost to Cruz by less than 3%. By 2020 I expect Trump to be further damaged than he is now. How will a politically damaged Trump fair against a hometown boy? We'll have to wait and see on that but I'm betting Trump won't do nearly so well next time around.
In Texas or anywhere else.
Beto might not actually flip Texas but it could be pretty close.

More than anything though, he brings some excitement into the race.
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"Be yourself; everyone else is already taken." Oscar Wilde