These counties have small population and non-hispanic white majority. However, the Democrats used to win these counties until 2000. When Gore won these counties, it was the last time a Democrat won a county in Texas outside the Hispanic South and the big cities. We can note also that in 2000, Bush had a wide margin in Harris and Dallas. So, the electoral map in Texas changed a lot in only 12 years.
What do Robertson, Morris and Newton counties have that is different from other counties in Texas?
Relatively large black populations automatically give the Democrats a higher "floor" there. They are all East and Central Texas counties with very strong Yellow Dog Democrat roots. They are also dirt poor and there are no suburbs or mid-sized cities in those counties where the GOP could have built a base of support from earlier. Even the white people are likely on food stamps and disability.
I used to drive through Robertson County when I'd go home from college. I recall there always being a dilapidated wooden house overlooking the highway with a large sign in the front yard that said "Had Enough? Vote Democratic!" At various times I recall seeing white people near the house and in the yard so my assumption was that they lived there and chose to put the sign up.
