If Texas Democrats hold the 12 House seats they gained in 2018 (shown in blue) and take the nine seats where Beto O'Rourke prevailed in the U.S. Senate race (light pink), they can flip the House in 2020 even without winning a single district carried by Ted Cruz. But there are 13 other districts (darker pink) where Zodiac prevailed by less than 10 points, which are thus within striking distance.

You'll see that in two of these, the Dems didn't even field a candidate in 2018. (That won't happen again.) How easy will it be to hold the 2018 gains? You'll see that not all of those races were very close, and for reference, the four Dems who picked up red seats in 2016 all won again last year by wider margins. Almost all of these races are in major metro areas, primarily Houston and DFW, plus the four Central Texas pickups from 2018 and some outliers in College Station, Corpus Christi, Killeen, and San Antonio.