The interesting thing about Texas, is even though it has more counties than any other state (254) the overwhelming majority of the population (80%) lives in basically five Metro areas (Houston, DFW, Austin, San Antonio, and El Paso) and then we could throw in a few other medium-sized cities like Corpus, Laredo, and Lubbock.
The vast majority of counties are not only relatively low-population, but also extremely inelastic, so although we might see some significant swings in counties with larger Latino populations for example in WestTex and parts of SouthTex, we won't see very many county flips despite what appears to be a major statewide swing away from the Republican margins in '08 and '12.
I don't think there is any question at all that Brewster & Kennedy will flip back from Obama '08 and Romney '12 considering the large Latino population.
Additionally, I think that Uvalde in West Tex that went McCain and Romney by 5-7 % will flip with a 66% Latino population, as well as Hudspeth (48 McCain and 44 Romney) that is 75% Latino.
I'll lay money down that Nueces (Corpus Christi) will flip. The "Texas Riviera" is one of the most beautiful parts of the Gulf Coast, and although it is heavily Latino these are precisely the type of Latino voters that frequently break Republican in Presidential and statewide races, but Trump is not the dude that represents their values, regardless of many employed working in offshore oil rigs that might be concerned about the environment vs jobs false dichotomy.
There might be some other rural counties that I missed in places like WestTex and SouthTex that might flip solely because of a complete collapse of Republican support among Tejanos and Latinos.
Moving to Urban/Suburban Texas:
Fort Bend I consider to be an automatic flip.... You have a rapidly growing Middle-Class suburban county of Houston that is rapidly becoming Blacker and Browner, not only in Pearland, but in many other parts of the county. Sugarland that was a traditional heavily Republican stronghold with extremely high household incomes for Metro H-Town is also a place that has one of the highest percentages of Asian-Americans in the region (Heavily Vietnamese-Americans) along with a boatload of college-educated Anglos that don't dig the Trump bag on so many issues.
Waller County is a mix of extremely rural redneck, and Upper-Middle Class Houstonians that are willing to take the long drive down SH-290, despite constant construction to trade off more house for longer commute. Honestly, I don't think Waller will flip but I do think that Clinton will exceed Obama '08 numbers.
Tarrant County (Fort Worth) is obviously ground-zero for Dems in Metro DFW. I don't see it flipping but Trump will likely only win by 4-5%.
Now we start moving into Central Texas:
Hays will almost definitely flip... San Marcos is exactly the type of town where college-educated Anglos will be dumping Trump en masse as the Republican nominee...
Williamson is definitely an interesting test of how College-educated Anglos move in Texas.
Round Rock, although it is part of the Metro Austin SMSA is also it's own bag. Dell Corp HQ is here, and is the biggest employer, as well as other spin-offs and suppliers tied to a sector and industry that is not only highly educated, but also increasingly international in terms of skilled "knowledge-sector employees" where Trump's rhetoric, economic policy positions, and so many other items don't play well. Although I won't predict this county flipping, I suspect it will be within a five point margin, in contrast to McCain +13 and Romney +26.
I'll throw in a few other counties that I think might flip, but still give Trump odds on:
Atascosa, Bee, Bastrop, and Bell.
Ok---- now after my long post looking forward to some Native sons and daughters of Texas to jump in on the potential county flips....
Not a native son, but four years in the Lone Star state gives me a few angles, so looking forward to any critique/feedback and comments where I might be full of absolute BS or on the money...