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.
Those races had Perot as a candidate.
