In deep-red Texas, Republicans will have to fight for every seat in Congress during next year's midterm elections. For the first time in 25 years, Democrats are running in all of Texas' 36 congressional districts, according to documents filed with the Texas Secretary of State's office.

Those filings set a record for the number of Democratic challengers in an era of Republican dominance, says Mark Jones, political science fellow at Rice University's Baker Institute. They are a departure from 2016, he says, when eight Republican-held congressional seats went uncontested by Democrats.

"We are seeing a groundswell of unusually high support and mobilization among progressive Democrats who are really angered by the Trump administration," Jones said.

Even though Democrats are more motivated than they've been in years, Texas remains a mostly Republican state. The GOP swept all the statewide races in 2016 and Donald Trump won the state by nine percentage points.

While the margin was closer than many years before, it's still a big gap for Texas Democrats to close.

Democrats aren't just gunning for congressional seats. According to preliminary numbers from the Texas Democratic Party, Democrats are running in 89 percent of the seats in the Texas House and 88 percent of the seats in the Texas Senate. Both are the highest percentages the party has mustered since at least 1992.

"We are seeing Democrats come out to run not only for the goal of challenging and doing something to voice their opposition to President Trump," Jones said. "But we are seeing Democrats come out in several districts where, in the past, Democrats had no chance whatsoever and had difficult time recruiting top-quality candidates."

Historically, the opposition party can make big gains in Congress during the first midterm election following a presidential election. For example, Republicans won back the U.S. House in 2010 after the election of President Barack Obama in 2008.

Jones says resistance to President Trump's policies has led to "enthusiasm and mobilization," particularly among more left-leaning Democrats. But he says that doesn't mean that Democrats can expect huge gains in dependably Republican Texas.

"Outside of [congressional district] 23, held by Will Hurd, all of the Republican-held districts today, more likely than not, will stay Republican-held districts," Jones said. "But they are not locks, and certainly we can't consider them to be sure-things."

Jones says it will take a perfect storm for Texas Democrats to make significant gains in Congress. He says Trump's approval ratings will have to continue to decline, Democrats will have to continue to out-fundraise their Republican opponents, and Republican candidates will have to make a lot of mistakes.

Tariq Thowfeek, a spokesperson with the Texas Democratic Party, says he's optimistic Texas Democrats could help the party take control of the U.S. House.

"Democrats need 24 seats to take back the House," he says. "I think four of those seats can come from Texas."

But Brendan Steinhauser, a Republican strategist in Austin, says flipping four Republican-held seats in Texas won't be easy.

"This has the potential to be more competitive statewide," says Steinhauser. "Although, I would think most Republicans would say that we are still probably not going to lose any incumbents this cycle."

Texas' congressional map doesn't favor Democrats. Federal courts have ruled the congressional map drawn by the GOP-led Texas Legislature intentionally discriminates against minority voters, which tends to hurt Democratic candidates. However, the U.S. Supreme Court has put a hold on the effects of those rulings as it weighs a gerrymandering case from Wisconsin.

Democrats could have a shot at unseating Republicans in congressional districts that Hillary Clinton won last year. Democrats are currently eyeing three of those districts, specifically:

All three of those incumbents have filed for re-election, and Steinhauser says he doesn't think they're as vulnerable as Democrats hope.

"Those three members of Congress over-performed Donald Trump on the ballot and they did win re-election," Steinhauser says. "So, if you are looking ahead to 2018, it does seem like they are going to win in 2018 given that Republicans do tend to do better in midterms than they do in the presidential years."

A lot of that depends on turnout, though. Steinhauser says the key for Republicans to keep their voters engaged is to deliver on some of their promises, including the GOP tax plan.

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