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In 31 of the state’s 150 Texas House districts, the top candidates for the Republicans and Democrats finished fewer than 10 percentage points apart in last year’s general election.

Those results provide a rough guide to the political battlefield in Texas in 2020: 18 of those seats are now held by Republicans and 13 are held by Democrats. A tighter description of competitiveness — districts where the parties’ top candidates finished fewer than 5 percentage points apart — narrows the list to 13 House districts, including seven now held by Republicans and six now held by Democrats.

Statewide, the average Republican candidate on the 2018 ballot outdid the average Democrat by 7.3 percentage points, according to an analysis of district-by-district election results compiled by the Texas Legislative Council.

The partisan split in the House is narrow enough to give partisans on both sides plenty to scheme about. Republicans hold 83 seats. Democrats hold 65, with special election runoffs in Democratic districts next month to decide the remaining two spots.

That narrow list of potentially close districts includes Republican state Reps. Rick Miller of Sugar Land, Bill Zedler of Arlington, Matt Shaheen and Jeff Leach of Plano, Dwayne Bohac of Houston, Morgan Meyer of Dallas and Angie Chen Button of Richardson. The Democrats on the list are all freshmen: State Reps. Gina Calanni of Katy, Michelle Beckley of Carrollton, Jon Rosenthal of Houston, Vikki Goodwin of Austin, John Turner of Dallas and Erin Zwiener of Driftwood.

Ten Republicans are in districts where their party’s statewide candidates won by more than 5 percentage points but fewer than 10, including Tony Tinderholt of Arlington, Ed Thompson of Pearland, Craig Goldman and Matt Krause of Fort Worth, John Zerwas of Richmond, Sam Harless of Spring, Jonathan Stickland of Bedford, Steve Allison of San Antonio, Lynn Stucky of Denton and Brad Buckley of Killeen.

Seven Democrats find themselves in the same situation: James Talarico of Round Rock, Rhetta Andrews Bowers of Garland, Abel Herrero of Robstown, Ryan Guillen of Rio Grande City, Julie Johnson of Carrollton, John Bucy III of Austin and Ana-Maria Ramos of Richardson.

One Democrat — Calanni — represents a district where Republicans, on average, won those statewide elections. Two Republicans are in districts where Democrats prevailed at the top — Bohac and Sarah Davis of Houston.

But no House Democrat has a district where Ted Cruz beat Beto O’Rourke. A number of Republicans, however, represent districts where Cruz lost: Allison, Stucky, Miller, Leach, Shaheen, Bohac, Button, Meyer and Davis.

Donald Trump defeated Hillary Clinton in six House districts where Democrats will be defending their seats: Zweiner, Calanni, Beckley, Rosenthal, Talarico and Goodwin. But Clinton won in these Republicans’ districts: Bohac, Button, Meyer and Davis.

The mix in the Texas Senate doesn’t appear to be in any kind of unusual trouble; only one of the seats that will be on the 2020 ballot — SD-19, where Republican Pete Flores scored a political upset last year and won in a district that typically favors Democrats. In the other 15 Senate districts on the 2020 ballot, the eight Republican and seven Democratic incumbents would be seeking re-election in districts dominated by their own parties.

It’s a testament to the partisan strength of the Senate’s redistricting maps. In Flores’ case, Cruz lost by more than 14 percentage points. In 2016, Trump lost by more than 11 points. And the average statewide Democrat beat the average Republican there by more than 10 percentage points last year.

That seat will be a hot spot for both parties; the rest could see primary fights but are less likely to flip in the general election unless the candidates make big mistakes.

On paper, that’s not enough to rock the Senate in 2020, either way. But with up to a fifth of the House seats in play, both parties have room for hope and terror. And with redistricting coming in the 2021 session, the partisans have something to fight over.

Disclosure: Sam Harless has been a financial supporter of The Texas Tribune, a nonprofit, nonpartisan news organization that is funded in part by donations from members, foundations and corporate sponsors. Financial supporters play no role in the Tribune's journalism. Find a complete list of them here.