The lines stretched in the dark across the plaza at Texas Southern University, as hundreds of would-be voters stood for hours Tuesday to cast ballots in the Democratic presidential primary.

As they waited, students shared phone chargers, activists sent in pizza and exhausted voters resorted to sitting on the ground.

The voting center at the historically black university in Houston was one of a number of such locations around Texas that were plagued by long delays on Super Tuesday, raising questions about the readiness of local election officials and spurring outrage among voting rights advocates. Many cited as a factor the closing of hundreds of precincts around the state after a pivotal Supreme Court decision in 2013.

One of the remaining Democrats in the presidential field — Sen. Bernie Sanders (I-Vt.) — seized on the episode, tweeting that it revealed a “crisis of voter suppression.”

However, interviews with election officials, activists and voters pointed to a number of complicated factors that combined to produce the massive lines in Harris County.

“There was actually a failure in the system at multiple junctures,” said Beth Stevens, the voting rights program director with the Texas Civil Rights Project, in an interview.

“The effect is that you have black and brown people on college campuses standing in line for two hours, four hours, seven hours to vote,” she said.

Harris County Clerk Diane Trautman, a Democrat elected in 2018, tweeted a message of thanks to voters Wednesday morning, saying: “There is no such thing as a perfect election, but I am committed to always improving the voting process and increasing access to the polls.”

Election officials noted that Tuesday was the county’s first primary using a countywide polling system, which allows residents to cast ballots at any polling center, regardless of where they live.

In addition to that change, the primary was shaped by the decisions of the local political parties, which were responsible for major issues such as where polling places were to be located, officials said.

“The Democratic and Republican Party need to agree on everything,” said Roxanne Werner, the director of community relations for the Harris County Clerk’s Office, in an interview. “All of the polling locations were negotiated by the Democratic and Republican Party with our assistance.”

Compounding the issue: Turnout was higher than expected, and because Tuesday was a primary, fewer polling locations were open than will be in November.

Werner said Harris County plans to have all of its polling locations open for the general election in November — about 750 polling places compared with 401 on Tuesday. She said the unusual role of political parties in Texas primaries makes it difficult to compare Super Tuesday to the November vote, which will be run entirely by professional election administrators.

“Primary elections are different. People don’t always realize the full scope of how they’re different,” Werner said.

Other factors contributed to the long wait times. Texas’s Harris County — which includes Houston and is the third most populous county in the country — relies on paperless voting machines that were introduced in 2002. They can be difficult to use and are prone to breaking down, according to election security experts. Several people said in interviews that the machines at TSU did not function consistently throughout the day Tuesday.

The voting exercise was also complicated by the Harris County Republican Party’s decision not to hold a primary jointly with the Democratic Party, officials said. This meant that each party had designated voting machines and that voters from the other party — even if they were waiting in long lines — could not cross over to use the other side’s machines.

Trautman noted in a tweet that she had proposed a joint primary but said “one party agreed while the other did not.”

Lillie Schechter, the chair of the Harris County Democrats, said that “a joint primary would have allowed us to use all the machines at each location for every voter that came in.”

“So when we had machines go down at TSU for a brief period of time, it wouldn’t have mattered, because voters would have been able to use all the machines,” she added.

Genevieve Carter, the communications director at the Harris County Republican Party, argued that a joint primary would not have prevented the long lines. She said that GOP’s decision to decline a joint primary reflected a lack of confidence in county election administrators.

“What this comes down to is the county clerk’s incompetence and even arrogance,” Carter said in an interview. “They have chosen to point fingers rather than fix the way that they went about elections.”

To some advocates, the lines were a sign of the long-term effects of the Supreme Court’s 2013 decision in Shelby County v. Holder. The ruling blocked federal oversight of certain regions of the country that historically had sought to limit the voting rights of minorities.

To restore the oversight, Congress must approve a new formula to determine which regions merit scrutiny. The Democratic-led House passed legislation last year, but the Republican-led Senate has not taken it up.

That has left large parts of the country without the robust federal protection of the Voting Rights Act of 1965.

“What we saw at TSU yesterday is really voter suppression in 2020,” said Vanita Gupta, the president and chief executive of the Leadership Conference on Civil and Human Rights, in an interview.

“In a lot of ways, I think the American public thinks it’s just conspiracy theory when we talk about this. But when you see images like yesterday and hear directly from impacted people who were standing in line . . . I think that the events of last night speak for themselves.”

In a study released last year, the Leadership Conference found that Harris County eliminated 52 polling places between 2012 and 2018, the fourth-highest number by a county in areas affected by the Shelby decision. At the state level, Texas led the way with 750 polling places closed.

Gupta pointed to this finding and to reports of the voting machines at TSU breaking down on Tuesday as “proof points that cry out for change.”

Trautman vowed after taking office in February 2019 to “fully comply with the requirements of the Voting Rights Act to protect all of the people of Harris County from the denial of their right to vote . . . particularly concerning the rights of people of color, members of language groups and persons with disabilities.”

On the TSU campus, freshman Marleta Haynes, 19, said she originally went to vote around 4 p.m. The line seemed long, so she figured she would come back later when it had shortened.

By when she returned, she said, she was shocked to see that the line now snaked across the campus. She waited for more than five hours, from 6:50 p.m. until midnight.

“On my feet the whole time,” she said. “I had to set an example for others, like my younger brother.”

After four hours of waiting, she finally stepped into the building where the voting machines were and saw that the line zigzagged farther inside.

“I was like, ‘Okay, I don’t think I can do this. I do not think I can do this,’ ” Haynes said. “But I started texting my friends, and they were like, ‘You’ve been waiting in line for too long; you cannot give up now.’ ”

Haynes said that by the time she left, she had missed the last shuttle to her off-campus student housing. Her phone was dying, so she had a friend call an Uber ride to take her home. It was not the first-time voting experience she had expected, but she said she will not be deterred. She’ll vote again in November, she said.

“But much earlier,” Haynes said. “When they tell us there is early voting going on, I will most definitely do that.”

TSU freshman Kim Rivers, 19, said she got in line when her class let out at 3 p.m. and waited for two hours to vote for former vice president Joe Biden.

Rivers thought it was unreasonable that there seemed to be the same number of voting machines for Democrats and Republicans.

“Being in an all-black community, you know there’s not many Republicans coming to vote,” Rivers said. “Especially on campus at an HBCU. So why do y’all have a whole five voting machines and only five for the Democrats?”

When she left for basketball practice later that night, she saw that the line to vote stretched to the student center and that people were handing out water bottles.

“It was terrible,” she said. “I’ve never seen a line so long to vote. That’s how you know it was important.”

Brittney Martin in Houston contributed to this report.