Why did Trump underperform in Texas relative to pre 2016 Republicans?

[Alben Barkley]

Heavy suburban swings against him in places like the DFW area. Biden flipped Tarrant, cut the margins heavily in Denton and Collin, ran up the score in Dallas proper, Austin, Houston, etc. Hillary and Beto had already done some of the work and he just continued those trends.

These suburban and college-educated white Democratic trends existed all over the country and are a big part of why Arizona and Georgia flipped outright. The South was not immune to them, and we’re seeing the education gap being more and more important as the racial gap becomes a bit less important. So even though Trump got big swings with Hispanics in the RGV, he still came closer to losing Texas than any Republican in years.

That’s also because of the numbers game; the places trending D rapidly are also those that are growing most rapidly while the places going the other way are stagnant or shrinking. That’s how Georgia swung over 5 points and flipped. If current trends continue in Texas (which voted about as R as GA did in 2016), it will flip eventually.

[Alben Barkley]

He didn't.

He did better than Ted Cruz, and he was supposed to match.

Houston 'burbs were more Trump heavy than expected, to say nothing of RGV.

According to whom?

He underperformed in both 2016 and 2020 relative to practically all other Republicans in Texas aside from Cruz in 2018 for the last 30 or so years. OP asked why that was and why he didn't win by double digits (which he didn't in 2016 either), not why he didn't match Cruz. And since 2018 was better for Democrats than 2020 practically everywhere except Georgia, Trump only doing 2 points better than Cruz is hardly what I would call an overperformance.

He overperformed the polls that had Texas as a total toss-up, yes, but that's about it. And the polls were off practically everywhere except, again, Georgia. And he still didn't overperform in Texas nearly as much as he did in states like Ohio and Iowa, or even Wisconsin and Michigan which he lost.