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Texas' gerrymanders are the political equivalent of putting houses on stilts to keep them safe from flooding.

Democratic hopes for a “blue wave” that would lift some of their candidates into statewide office and reduce their disadvantages in the congressional delegation and the statehouse aren’t completely out of line. Presidents’ political parties often have trouble in midterm elections.

It’s just that Republicans in Texas drew maps in 2011 — since modified by the federal courts but still being litigated — that protect the party’s officeholders from most changes in public sentiment.

Thanks to those very effective Republican redistricting maps, Texas Democrats would have to improve their statewide election results by more than 10 percentage points to gain more than one seat in the 36-member U.S. House delegation, according to a report from the non-profit Brennan Center for Justice.

The political maps in Texas and elsewhere across the country could ultimately protect the Republican majority in the U.S. House even if it turns out to be an otherwise mediocre midterm election for the president’s political party.

Overall, Republicans have a 24-seat advantage in the U.S. House. Democrats have an advantage over Republicans in recent polling, the report says, but gerrymandering makes a party switch much less likely. To win two dozen seats, by Brennan’s figuring, Democrats would have to win the national popular vote by 11 percentage points.

“Even a strong blue wave would crash against a wall of gerrymandered maps,” the report says.

The 2016 elections put 25 Republicans and 11 Democrats in the state’s delegation to the U.S. House. Democrats got 42 percent of the state’s votes that year, according to the report’s authors. A modest improvement in the share — as little as 2 percent — could move a seat from the Republicans to the Democrats. It’s not hard to figure out that the 23rd Congressional District that runs along the border is what’s in play here; it’s the only true swing seat in the state, regularly primed to go to whichever party is having the better election year.

But here’s the house-on-stilts aspect to the maps. According to the Brennan Center’s projections, the Democrats could improve their statewide vote share by as much as 7 points — to 49 percent — and that’s still the only congressional seat they would pick up.

Listen carefully right now and you’ll hear protests from other parts of the state, like CD-32 in Dallas and CD-7 in Houston, where optimistic Democratic challengers are vying to unseat Pete Sessions and John Culberson. They might be right. The study isn’t trying to predict races. It’s trying to show how strongly the Republicans cemented their advantage in Texas, given normal conditions. Actual mileage may vary.

It would take a tsunami — a double-digit leap in Democrat’s percentage share — to gain more than a single seat in Texas. Something like that would still leave the Republicans in the majority, but it would be a 19-17 advantage instead of the 25-11 edge they have now. “For Democrats to win more than one-third of seats under the 2011 Texas map, they would need to win close to half the vote,” the report says.

For what it’s worth, it’s unlikely the Republicans will increase their lead either. The Democratic vote share would have to slide to around 35 percent for that to happen. The trick to the current maps is that the middle zone — that 10 percentage point spread between Democrats and Republicans in the 2012, 2014 and 2016 elections — is protected. The popularity of the parties can swing that much with only one congressional seat in play.

“Putting even a few seats in play would require Democrats to win a larger share of the vote than they have all decade,” the study says.

Those mapmakers managed to disconnect votes from election outcomes. Instead of drawing maps that are sensitive to changes in voter sentiment, Texas lawmakers (and the judges who changed some of those legislators’ lines) drew maps that resist anything but the largest swings in the public mood.

The GOP’s political house could still flood, but that would take a record-breaking blue tide.