The 2018 congressional election season has officially begun, and Tuesday brings the first congressional primaries of the season, in Texas.

If the state attracts any political drama, it’s normally centered on Republicans. And there’s some of that going on right now, especially in a congressional primary battle between Trumpers vs. a Never-Trumper.

But the real drama on Texas primary day is happening on the left this time. Democrats consider this year a pivotal marker in their efforts to turn Texas purple or even blue, and yet they can’t decide on the best way forward.

If there is to be a Texas version of a Democratic wave this November (defined by picking up one to as many as five congressional seats and 10 state House seats), Tuesday could bring early signs of it. For the first time in at least 25 years, Texas Democrats have put up a candidate in every one of the 36 congressional seats. Early voter turnout for Democrats has doubled from 2014 levels, and in some places even rivals turnout during the 2016 presidential primary.

One political operative predicted that turnout for Democratic primaries could equal turnout for Republican primaries, suggesting there are just as many Democrats as Republicans willing to vote in November in Texas.

“If Texas votes like it looks, then Democrats win,” said Manny Garcia, deputy director of Texas Democrats, “and Democratic enthusiasm is through the roof right now, so that we are changing the political landscape very quickly.”

But amid all the positive signs, Washington Democrats launched an all-out war against one of their party’s candidates for a congressional seat in the Houston suburbs, concerned that Laura Moser could win the primary and lose a winnable seat for them.

Some of this intraparty drama could impact the really big race coming up for Texas Democrats this year in the U.S. Senate. Sen. Ted Cruz (R) is running for reelection and facing a credible challenger in Rep. Beto O’Rourke (D) from El Paso. Election forecasters say Cruz is more likely to win than not in November, but at the very least the race will be a test of whether and when it’s possible for Democrats to win statewide in Texas. O’Rourke is going to need all the help from his party he can get: Texas hasn’t sent a Democrat to the U.S. Senate in 30 years.

Rep. Beto O'Rourke (D-Tex.), who is running against Sen. Ted Cruz (R) for a Senate seat, speaks to a customs agent as he crosses into El Paso from Juarez, Mexico, in February. (van Pierre Aguirre for The Washington Post)

With all that as the backdrop, here’s a rundown of four key primary races to watch in Texas on Tuesday. We’ll start with the Democrats.

1. Democrats are in a war about who should challenge one off Texas’s most vulnerable Republicans

Laura Moser is running for Congress as a progressive Democrat. (Michael Stravato for The Washington Post)

It’s no surprise that Democratic infighting is concentrated on this seat. It’s one of their best pickup opportunities among congressional races. Rep. John Abney Culberson (R) represents the northwestern Houston suburbs, a district that went for Hillary Clinton over Donald Trump by one percentage point in the presidential election.

Progressive activist and author Moser really was in the second tier of Democratic candidates to earn her party’s nomination to challenge Culberson in the 7th District. But that may have changed a few weeks ago, when the Democratic Congressional Campaign Committee published a scathing opposition research paper on her, highlighting the fact that she wrote in 2014, “I’d rather have my teeth pulled out without anesthesia” than move to rural Texas.

Democrats’ aggressive move against one of their own candidates made national headlines and exacerbated a party split that still hasn’t healed from the 2016 election. Progressive groups accused the DCCC of meddling in races it doesn’t understand. “They’re certainly not out there earning the trust of voters by attacking a pro-choice Democratic woman in the race,” Democracy for America electoral director Annie Weinberg said. The DFA has endorsed Moser.

Will grass-roots energy and national headlines be enough to push Moser to at least the top two? (Texas has a runoff system, where a candidate must get more than 50 percent of the vote, or the top two face off in a May 22 runoff.)

We’ll find out Tuesday. Moser is one of six candidates on the Democratic side, with the front-runners generally considered to be attorney Lizzie Pannill Fletcher and nonprofit executive Alex Triantaphyllis.

2. In El Paso, could Democrats nominate the first Latina member of Congress from Texas?

Former El Paso County judge Veronica Escobar in her office in November. (David Weigel/The Washington Post)

One crowded primary Democrats generally aren’t fighting about is the race to fill O’Rourke’s seat in El Paso, which he vacated to run for Senate.

A number of liberal groups have endorsed former El Paso County judge Veronica Escobar over four other candidates. “Escobar is also in a position to make some long-overdue history: She would be the first Latina ever to represent Texas in Congress,” Carolyn Fiddler wrote at the liberal Daily Kos.

The winner of this primary — whether outright Tuesday or in a May runoff — will probably be the next member of Congress from Texas’s 16th Congressional District, given it’s one of the most pro-Democratic districts in the state.

3. A perennially competitive race along the border also has Democrats torn

Rep. Will Hurd (R-Tex.) faces a competitive election in his border district. (Melina Mara/The Washington Post)

The 23rd District, which extends from San Antonio nearly to El Paso and covers 40 percent of the U.S. border with Mexico, flips back and forth from Democrat to Republican nearly every election cycle.

Rep. Will Hurd (R) has managed to hang onto the seat for two elections. This year, Texas Democrats are hoping that President Trump’s unpopularity will sink Hurd. (At 39 percent, Trump’s approval rating among Texans is the lowest in a Republican state, according to a January Gallup survey)

The field of four Democratic challengers is splintered.

Gina Ortiz Jones, a former Air Force intelligence officer, is exciting some liberal groups, such as Emily’s List, not least because of her firsts: She would be the first openly lesbian veteran in Congress. Consider former federal prosecutor Jay Hulings the establishment candidate. He has the endorsements of the Congressional Hispanic Caucus and one of the state’s most well-known Democratic congressmen, Rep. Joaquin Castro.

A Bernie-Sanders aligned group, Our Revolution, has backed schoolteacher Rick Treviño.

4. An insanely crowded Republican primary outside San Antonio and Austin

There are 18 Republicans trying to run for a seat being vacated by retiring Rep. Lamar Smith (R). And most of them, reports The Washington Post’s Mike DeBonis, are taking the strategy of: There’s no such thing as being too close to Trump. “Make America Like Texas” slogans, TV ads of candidates literally standing in swamps promising to drain them — this race has it all, except for a clear front-runner.

Watch for whether a Ted Cruz-backed candidate wins. Chip Roy, a former Cruz aide, benefits from his Washington ties, with super PACs running ads in which Cruz calls Roy the “real conservative.”

And then there’s the lone Never-Trumper. Jenifer Sarver is a former George W. Bush official who voted for Hillary Clinton and, DeBonis reports, “is unapologetically calling for a more inclusive GOP and more distance from Trump.”

[2018 Texas primaries: Live Senate, Governor and House results]