Mr. O’Rourke’s close result wasn’t because of an exceptional turnout that will be hard for other Democrats to repeat in 2020. Republican voters, defined as those who have participated in a recent Republican primary, turned out at a higher rate than Democratic ones. Neither the Hispanic nor youth voter share of the electorate was higher than it was in 2016, when President Trump won the state by nine points.

On the contrary, Democrats in 2020 can be expected to enjoy a more favorable turnout because presidential races tend to draw in more young and Hispanic voters. Mr. O’Rourke might have won Texas last November if turnout had been at the level of a contested presidential race, based on an Upshot analysis of Times/Siena poll responses, actual results and voter file data from L2, a nonpartisan voter file vendor.