As measured by job creation and population growth, the “Texas Triangle” bounded by Dallas-Fort Worth, Houston, and San Antonio-Austin is the strongest economic region in the United States. While Houston is the hub of the U.S. energy industry, big tech companies are settling in Austin (Google and Apple) and Dallas (Uber).

And with a large, young, and college-educated workforce flocking to live and work in the region, these Texas cities and suburbs have been both gaining political power and becoming more solidly liberal. Research by Renée Cross and Richard Murray at the University of Houston has found that voters in the 27 counties around big metro areas grew from 52% of the total electorate in 1968 to 69% in 2018. Meanwhile, voters in the more rural counties – outside the Democratic strongholds in south Texas – decreased from 38% to 8% in that time.

Mr. O’Rourke in particular was effective in ginning up support and – crucially, for a low-turnout demographic – votes from young Texans. He carried the state’s five major urban counties by a combined 790,000 votes last year, six times more than Mr. Obama in 2012. Registering and turning out more voters in those cities and suburbs is at the core of Texas Democrats’ plan, released this week, to flip “the biggest battleground state in the country.”