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.

Democratic candidate 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, 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, 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.

The primary also was shaped by 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.

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.