News analysis

Democrats haven't won statewide office in Texas since 1994. But recently, there have been subtle signs the GOP's stranglehold on the Lone Star State may be loosening.

In 2016, Donald Trump carried it by just 9 percentage points, less than his margin in Iowa. In an average of its 2017 surveys, Gallup pegged Trump's approval rating in Texas at 39 percent — lower than any other state he carried. And in 2018, Democrats are fielding candidates in every one of Texas's 36 House seats for the first time since 1992.

These factors have given some Democrats hope that if 2018 turns into a "blue wave," they could cut into Republicans' 25-11 edge in Texas House seats and possibly even give GOP Sen. Ted Cruz a run for his money. But it may be premature to repaint this red state purple.

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On Tuesday, Texas kicked off 2018's congressional primaries, and in a positive sign for Democrats across the country, their voters demonstrated far greater energy than in past midterms. With nearly all votes counted, total votes cast in the Democratic primary surged 85 percent over 2014's tally, compared to a 14 percent increase on the GOP side. However, the Republican primary still accounted for 60 percent of all primary turnout.

Democrats' enthusiasm gains over 2014 and 2010 were especially pronounced in wealthy inner suburbs of Houston and Dallas, where Trump is uniquely unpopular. That's good news for Democrats' hopes of unseating GOP Reps. John Culberson and Pete Sessions, neither of whom have faced competitive races this decade. Their districts handily voted for Mitt Romney in 2012, but in a surprise, Hillary Clinton narrowly carried both districts in 2016.

However, Democrats' gains were much less pronounced in small-town and rural Texas. And Democrats' new Senate nominee, Rep. Beto O'Rourke, a former punk rocker who represents El Paso, showed he still has work to do to consolidate his own party before he faces Cruz. He demonstrated far less appeal among his own party's voters in places like Beaumont (34 percent), Laredo (42 percent) and Dallas (58 percent) than he did in liberal Austin (87 percent).

So is ruby red Texas starting to drift toward becoming a purple state? Whether or not Democratic candidates break through at the state or district levels in 2018, the long-term trend line suggests it's quite possible.

For a generation, despite the state's booming nonwhite population, Republicans' advantage in Texas barely budged. From 1980 to 2012, the Census estimates that the Hispanic share of Texas' population surged from 20 percent to 37 percent. Yet in 2012, Mitt Romney won 58 percent of all major-party presidential votes cast in the state — a point higher than the 57 percent share Ronald Reagan won in 1980.

The reason Texas stood still could be explained by two offsetting trends: As Democratic-leaning Hispanics and African-Americans grew in voting strength, Republicans made enormous gains with rural whites who felt increasingly alienated by coastal liberals.

But in 2018, Republicans may be on the verge of "maxing out" their shares of rural whites. In 2016, exit polls showed Trump winning 76 percent of Texas whites without college degrees. Meanwhile, the nonwhite share of eligible voters is continuing to rise every year. And even more important for Democrats, Trump has alienated a booming, traditionally GOP group: suburban professional whites, especially women.

Democrats' new energy in the suburbs is unlikely to help O'Rourke or other 2018 statewide Democratic candidates if, as in past midterms, nonwhites fail to show up. According to the Census Bureau, nonwhites made up 41 percent of Texas' electorate in 2012 and 39 percent in 2016, but just 35 percent in 2014.

No matter what happens in those races, however, Texas will make history in 2018. Incredibly, Texas has never elected a Latina to Congress. But on Tuesday, Veronica Escobar, former El Paso County judge, and state Sen. Sylvia Garcia both won their primaries with more than 50 percent of the vote (the threshold needed to avoid a runoff), virtually guaranteeing they will win safe Democratic seats in El Paso and Houston this fall.

David Wasserman, House editor for The Cook Political Report, is an NBC News contributor and senior analyst with the NBC Election Unit.