SAN ANTONIO — For a quarter-century, Republicans have dominated Texas politics so much that the Democratic minority has often been an afterthought. The big political battles in Austin have been fought between conservative and centrist factions within the GOP, as Democrats watch from the sidelines.

But Democratic gains in this year’s midterm elections on the federal, state and county level show the prospect that Texas will become a swing state — a promise Democrats have made for years — is slowly coming to fruition.

Texas’s evolution illustrates two of the defining inflection points in American politics today: A growing divide between liberal urban cores and conservative rural bastions; and a shift in attitudes of suburban voters turned off by President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE and his Republican Party.

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Those factors have helped turn states like Nevada and Colorado blue, as large metropolitan areas like Las Vegas and Denver dominate more conservative rural areas. At the same time, they have pushed states like Pennsylvania and Michigan toward purple status, as the once-dominant metro areas like Philadelphia and Detroit lose population and political influence.

In fast-growing Texas, both of those fulcrums are tipping toward Democrats.

Hundreds of thousands of new residents are moving into Texas every year, choosing to live in fast-growing cities and suburbs around the state’s four largest metropolitan areas. Six of the nation’s 10 fastest-growing counties are in Texas. About one in every 10 Texas residents did not live in the state when Sen. Ted Cruz Rafael (Ted) Edward CruzCruz blocks amended resolution honoring Ginsburg over language about her dying wish Trump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP MORE (R) first won his seat six years ago.

“We have a lot of new voters who have held up their hands. There’s thousands of new voters moving to Texas every week,” said Chris Homan, a veteran Texas Republican strategist.

Those new residents are changing the partisan hue of once-reliably Republican suburbs and fueling a massive surge in new voters in solidly Democratic urban cores that even Republicans acknowledge will put the state’s massive haul of electoral votes in play for the first time in a generation.

“Texas is a state that Democrats have been eyeing for some time now, because at the presidential level, it just keeps moving toward Democrats,” said Ethan Roeder, who ran data analytics for former President Obama’s 2008 and 2012 campaigns and who now works for the Democratic outside group Forward Majority.

This year, Democrats scored big wins in the fastest growing cities in Texas. The party won a dozen seats in the state House, mostly in clusters around Dallas and Houston. Forward Majority spent $2.2 million on those legislative races.

Voters in Harris County, where Houston sits, kicked out a three-term Republican county executive in favor of a 27-year old political neophyte. Nineteen black women ran for judgeships in Harris County; they all won.

Those gains in big cities came from a remarkable surge in turnout, and a realignment that shows just how solidly Democratic urban cores in Texas and around the nation have become.

In Harris County, Republicans won the straight-ticket vote by 9 points in both 2010 and 2014. This year, Democrats outperformed Republicans in straight-ticket votes by 11 points.

Democrats won the straight-ticket vote in Dallas County by 1 point in 2002, by 7 points in 2006 and 2010, by 10 points in 2014 — and by 30 points this year. Straight-ticket voters in Travis County, home of liberal Austin, chose Democrats this year by a 45-point margin, as turnout among those voters nearly tripled from 2014.

“Urban Texas is home to a vast majority of the state’s population, so this is where future elections will be fought,” said Brandon Rottinghaus, a political scientist at the University of Houston. “Republicans are losing that war to date. If Republicans can’t keep Democratic numbers below 60 percent in urban Texas, winning elections is going to be much more difficult going forward.”

Almost half a million new voters cast their midterm ballots early in Texas this year, as did more than a million voters who do not typically show up in midterms, according to the Democratic data analytics firm TargetSmart. Election Day turnout figures, when they are officially released in coming months, are likely to increase those numbers by hundreds of thousands.

“Texas has not been a red state. It’s been a nonvoting state,” said Rafael Anchia, a Democratic state representative “And when there’s large voter turnout, which overwhelms the gerrymandering efforts and voter suppression efforts of past cycles, it is very decidedly a purple state.”

What worries Republicans even more is a slower moving shift in suburban attitudes. The counties that surround San Antonio, Austin and Dallas are some of the fastest-growing in the country, and the thousands of new voters who move there are not as conservative as those who have lived in Texas all their lives.

Cruz won Denton County, just north of Dallas, by 32 points in 2012, when he first won his seat. Trump beat Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE there by 20 points. Cruz carried Denton again in 2018 — but by just 7 points.

Cruz won neighboring Collin County by 32 points in 2012. Trump won it by 16, and Cruz carried it this year by 6 points.

Cruz’s opponent, Rep. Beto O’Rourke (D), carried five counties that Cruz won six years ago, including Harris County and neighboring Fort Bend; Williamson and Hays counties, in the Austin suburbs; and Tarrant County, next door to Dallas.

The shifting suburbs will put some Republican members of Congress on Democratic target lists in 2020. Rep. Kenny Marchant Kenny Ewell MarchantHouse Ethics panel recommends ,000 fine for Rep. Schweikert's campaign finance violations Candace Valenzuela wins Texas runoff to replace retiring Rep. Marchant Ethics Committee reviewing Rep. Sanford Bishop's campaign spending MORE (R) won reelection to his suburban Dallas-Fort Worth seat by just 3.2 percentage points. Rep. Michael McCaul (R) won another term in his district, which bridges the suburbs of Austin and Houston, by just 4 points.

Rep. John Carter John Rice CarterDonna Imam wins Democratic runoff to face Rep. John Carter House panel advances bill banning construction on bases with Confederate names Democrats see victory in Trump culture war MORE (R) fended off a well-financed Democrat to hold his seat along Interstate 35 by three points. Three new members of Congress, Reps.-elect Dan Crenshaw (R), Chip Roy (R) and Ron Wright (R), all won their seats by fewer than 10 points.

“There were a number of other seats that were unexpectedly close,” Anchia said. “As you’re looking at the electoral map, there were a bunch of Democrats who didn’t win but who came really close in districts that were not perceived to be competitive.”

Both Democrats and Republicans credited two specific campaigns for boosting turnout, fueling Democratic wins at the legislative and local level while Republicans once again swept statewide races.

The two sides said O’Rourke’s campaign pushed thousands — probably hundreds of thousands — of new voters to the polls in the state’s largest cities. They also credit Gov. Greg Abbott (R), who launched a major field campaign even in more sparsely populated rural parts of the state, votes that benefitted Cruz as well.

There are few signs that Texas’s population explosion will slow any time soon. The state is expected to gain two or even three new House seats in the decennial reapportionment process, according to the demographer Kimball Brace.

If suburban voters continue their march toward Democrats, and urban voters continue their march to the polls, Trump and his Democratic opponent are likely to see Texas as an emerging battleground.

“Texas is in play for a presidential election,” Homan said. “The candidates we have, the campaigns we run, our ability to talk to a voting population beyond a narrow primary population, what we do in the next two years is going to define how Texas looks for the following 10 years.”

— This report was updated at 8:36 a.m.