Why has Colin County trended so much to the left while Montgomery hasn't budged?

[lfromnj]

Collin is more heavily inner-ring suburbs--more Fort Bend than Montgomery as far as distance from the central city is concerned.

What is the "Montgomery" of Dallas then?

The counties surrounding the big 4.

[lfromnj]

For some reason, no one ever mentions the absolutely staggeringly large Asian American population (10%!) in Collin County when discussing its demographics.

Isn't that mostly Vietnamese, who are an R-leaning demographic?

Its lots of Indians. IIRc planes 6% Indian and vietnamese would actually explain the 2012 to 2016 swing considering Romney won them in 2012 bt 10 but Trump lost em by 30.

[lfromnj]

Also Montgomery county has even started moving left really. Trump only had a 500 worse vote margin than Mittens,