Tonight’s Democratic Debate: Live Updates From Houston

How to watch: 8 p.m. to 11 p.m. Eastern on ABC, Univision and on streaming services.

Moderators: The debate will be hosted by George Stephanopoulos, David Muir, Linsey Davis and Jorge Ramos.

Candidates: Former Vice President Joseph R. Biden Jr., Senator Elizabeth Warren, Senator Bernie Sanders, Senator Kamala Harris, Mayor Pete Buttigieg, the entrepreneur Andrew Yang, Senator Cory Booker, former Representative Beto O’Rourke, Senator Amy Klobuchar and former housing secretary Julián Castro.

Texas Democrats are hoping for a blue wave.

It is the presidential campaign that brought hundreds of reporters and photographers to this sprawling, and still-steamy-in-September, city. But while Texas Democrats are happy to host the third presidential primary debate, it is not the White House race that many of them are most excited about.

One year after they beat a pair of veteran House Republicans, Democrats here are downright giddy about the possibility of picking up even more seats in 2020. That’s because of what has been called the “Texodous” — the decisions of five, so far, House Republicans from Texas to retire rather than seek re-election.

“They see the handwriting on the wall,” said Gilberto Hinojosa, the Texas Democratic Chair.

Three of the G.O.P. lawmakers who are retiring had won re-election by only five points or less and hail from districts filled with the sort of suburban and nonwhite voters who are uneasy with President Trump and are nudging this state toward the political center.

Even though he won Texas by nine points, Mr. Trump’s standing has plummeted in Texas: a new Quinnipiac poll found that 50 percent of the state’s voters disapprove of his job performance and 48 percent said they would definitely not vote for him next year.

While few officials in either party believe Democrats could capture the state from Mr. Trump next year, their prospects up and down the ticket here could depend in part on who they nominate.

And Mr. Hinojosa said most Texas Democrats were less focused on policy issues than who can make the best case against Trump. “They want a candidate that can beat him,” he said. “That’s the number one priority.”

But as for his own priorities, Mr. Hinojosa said he was more focused further down the ticket.

“Our main goal in Texas right now is to flip the state House,” he said, noting that many of the nine seats they are hoping to pick up in the legislature are in those same suburban districts where they may be able to win more congressional races.

And why is he so focused on state house races going into a year when Democrats have a chance at the White House? Because if Democrats control one chamber of the legislature they could at least slow Republican attempts to redraw legislative boundaries for another decade after next year’s census.

‘You can expect the candidate to take on Donald Trump.’

That’s the word from most, if not all, the Democratic nominees and their campaigns on Thursday, no one wanted to detail exactly how they were preparing to differentiate themselves from each other. In Houston, where several candidates and their staffs happen to be staying at the same hotel in the downtown area, the matchup of Mr. Biden, Mr. Sanders and Ms. Warren is the talk of happy hours and pre-debate events.

But it’s the candidates outside the top three that are promising the most fireworks.

Ms. Harris, Mr. Booker and Mr. O’Rourke are trying to present themselves as the most future-oriented candidates. Ms. Harris is expected to go on offense. Mr. O’Rourke will focus on offering a generational alternative to his establishment rivals, and Mr. Booker is likely to pitch similarly unifying themes.

If that sounds familiar, it’s because Democrats say they want to resist the urge to pit themselves against one another. So how will audiences get differentiating moments? We have three hours of debate to find out.

Will Elizabeth Warren be among the hunted?

For months, Ms. Warren has risen through the polls without much interference from the other candidates seeking the 2020 Democratic presidential nomination. Rivals praised the plans she offered, even as they chafed at having to always answer questions about them.

That time is near an end.

There has been a marked shift lately on how others in the field — particularly those far behind her in the polls — approach Ms. Warren, with increasing skepticism about her battery of policy proposals.

“This election is not just about our plans, it’s about our heart and gut,” Mr. Booker said Saturday in New Hampshire.

The tougher questions Ms. Warren will face are about whether she is too liberal to win a general election. Mr. Buttigieg calls for “real solutions, not more polarization” in an Iowa TV advertisement he debuted this week. Ms. Klobuchar said in an interview this week that “you don’t just want to win, you want to win big.”

The problem for the low-polling candidates is that Ms. Warren has now established herself as the candidate of ideas — ideas Democrats like. Along the way she has become very popular herself, a figure they may have allowed to become too imposing to take down.

The top four candidates’ best moments at the summer debates …

Biden: After a shaky performance in the first debate, Mr. Biden was somewhat steadier in his second appearance, including when he reached for a classic Bidenism to respond to talk from his opponents about “Medicare for all” and the failings of the current health care system. “This idea is a bunch of malarkey,” he said, before warning about what a Medicare-for-all system would cost.

Harris: Ms. Harris’s attack on Mr. Biden over race and busing gave a jolt of energy to her campaign, attracting a surge in donations and a bump in the polls. By invoking her personal story, Ms. Harris also contrasted herself as a young, fresh face in the Democratic Party, as opposed to Mr. Biden’s elder statesman status.

Sanders: Mr. Sanders has put a big focus on his signature policy proposal, creating a Medicare-for-all system in the United States. “I wrote the damn bill!” he declared during the second debate. He has not let voters forget it: He has used the line many times on the campaign trail since then.

Warren: Ms. Warren found a convenient foil in John Delaney, the former Maryland congressman, who argued in the second debate that the progressive policies she advocates were unrealistic. Ms. Warren’s candidacy revolves around the idea of fighting for sweeping change, and her comeback to Mr. Delaney — expressing bafflement about why someone would run for president with a message of discouraging big ideas — packed a punch.

… These were their most memorable lines …

Joe Biden

‘Anyway, my time is up’

Bernie Sanders

‘I wrote the damn bill!’

Elizabeth Warren

‘I don’t understand why anybody goes to all the trouble of running for president of the United States just to talk about what we really can’t do and shouldn’t fight for.’

Kamala Harris

‘That little girl was me’

What were their worst moments?

Biden: Mr. Biden was on the receiving end of the most memorable attack in the debates so far, when Senator Kamala Harris of California confronted him over his comments about segregationist senators and his record on busing.

Harris: In the second debate, Representative Tulsi Gabbard of Hawaii targeted Ms. Harris with a fierce attack on her record as a prosecutor. Ms. Gabbard said Ms. Harris owed an apology to “the people who suffered under your reign.” Though Ms. Harris has defined herself as a “progressive prosecutor,” Ms. Gabbard’s attack highlighted a part of Ms. Harris’s career that can be wielded against her in the primary race.

Sanders: During an exchange about climate change at the first debate, Mr. Sanders raised his hand to signal that he wanted to speak. But the moderators ignored him and turned instead to John Hickenlooper, the former governor of Colorado. The moment typified the night for Mr. Sanders, who at times all but disappeared from the conversation even as his ideas took center stage at the debate.

Warren: Ms. Warren made it through the first two debates without any glaring missteps. But one moment could be used against her in the future: when she raised her hand in support of abolishing private health insurance. A supporter of Medicare for all, Ms. Warren makes no apologies for taking that position. But her stance could provide ammunition to those seeking to paint her as too extreme in her progressive policies, including President Trump if she were to become the Democratic nominee.

Buttigieg needs a standout moment.

In the first debate, Mr. Buttigieg defended his record on race relations at the South Bend Police Department. In the second one, he faded into the background while Ms. Warren and Mr. Sanders owned the conversation about health care.

Now, as his campaign begins spending down his field-leading financial war chest, Mr. Buttigieg’s debate challenge is to shift from curiosity to serious candidate. He’s been a nonentity the first two times Democrats have debated in the presidential primary and he can’t afford a third tepid showing.

The challenge for the 37-year-old is how to present himself as a breath of fresh air and steward for a new generation of politics without getting his hands dirty by attacking others onstage. His contrast with Mr. Biden is implicit — the former vice president is nearly 40 years older — but if he is going to make the argument that he can build a broader coalition than his more liberal opponents, that may require some explaining to a still-skeptical electorate.

If other candidates are itching to go after Ms. Warren, Mr. Sanders has shown no inclination to squabble with the other leading liberal in the race.

At his debate preparations in Colorado this week, Ms. Sanders has focused on what he has been talking about his entire political career: limiting the power of corporations, installing a single-payer health care system and requiring billionaires to pay more to subsidize a broader social safety net.

That’s not likely to draw him into much of a contrast with Ms. Warren, but it may lead him into a fight with Mr. Biden, either as a tag-team partner with Ms. Warren or on his own.

Mr. Biden, aside from ideological differences, is Mr. Sanders’s chief competitor for Democratic primary voters. Their supporters tend to be lower-income, less educated and far less tuned in to the day-to-day machinations of the presidential campaign than those who back candidates like Ms. Warren or Mr. Buttigieg.

So for Mr. Sanders, a clash with Ms. Warren does less good than showcasing his ideological contrast with Mr. Biden and peeling support away from the former vice president.

Kamala Harris looks for momentum, not a moment.

Unlike many onstage in Houston, the question for Ms. Harris is not whether she can have a breakout moment. She can. She already has. The question — a harder one to answer — is whether she can turn a strong debate performance into sustained political momentum.

Ms. Harris’s first debate takeover of Mr. Biden of his past work with segregationists and busing led to a quick rise in the polls that quickly faded.

In the second debate, Ms. Harris arrived as the subject of attacks herself — most sharply by Representative Tulsi Gabbard of Hawaii, who will not be onstage this week — and delivered a more uneven performance.

Ms. Harris has herself among the top-tier candidates but that is the kind of phrase often best left for others to utter. Her mandate on Thursday is to show that to be the case, and then have public polling demonstrate the same.

Jonathan Martin and Astead W. Herndon contributed reporting from Houston.