"We attribute the lines to an unusually high and enthusiastic turnout at several locations due to the national platform," Roxanne Werner, communications and voter outreach director for the Harris County clerk's office, wrote NBC News in an email. She noted that the county experienced more in-person votes than during the early voting period.

But with the supercenters, it's easy for officials to misjudge how many vote centers are needed or put them in the wrong place or overestimate how much early voting you get. You could end up with taxed resources and long lines, which may have been what happened tonight.

Vote centers let voters vote anywhere. They can vote on their lunch breaks. They're supposed to increase voter turnout. There's no hurdle by getting your location wrong or not knowing where to vote. They're also popular in Texas. Over 50 counties use them, known there as "countywide polling places."

There's a common link between the long lines in Los Angeles and Harris County, Texas: Both switched from a "precinct-based" system to a one-stop "vote center" model, Eddie Perez, global director of technology development at the OSET Institute, a nonprofit that conducts election technology research, told NBC News.

This is INSANE. These people have been waiting in line to vote for five hours at TSU. Polls closed 4.5 hours ago. pic.twitter.com/PLEJxixini

My East LA polling place just got a pizza delivery. 45 minutes past polls closing but still an hour+ wait to vote. Probably more. pic.twitter.com/crS9JBoQgG

Trump camp publicly batting down Joe-mentum but privately concerned

We know President Donald Trump has been watching the Super Tuesday returns roll in — he predicted earlier that it would be an "interesting evening of television" — as he goes after both Mike Bloomberg and Elizabeth Warren on Twitter.

The self-styled political pundit-in-chief has acknowledged that Joe Biden has been looking better than observers initially expected before South Carolina, but his campaign is working to bat down any Joe-mentum.

"Everyone should remember that he is just as terrible a candidate right now as he was a few days ago," Trump campaign manager Brad Parscale said tonight, also echoing the president's accusation today that "establishment Democrats" are trying to rig the nomination against Bernie Sanders.

Despite the public bravado, those close to the president have long been concerned privately about a head-to-head matchup against Biden in the general election, specifically in key Rust Belt states, and that remains the case this evening, though of course we're a long way off from knowing whom the Democratic nominee will be.

And that's something Team Trump is seizing on — the expected chaos if, in fact, Democrats end up barreling into a contested convention. The longer the Democratic fight plays out, the better it is for the president in the eyes of his advisers, who tonight are seizing on a "splintered" Democratic Party. Watch for Trump allies to start to concentrate their fire on Sanders and Biden moving forward.

As we talk about what's next, keep this in mind: For the first time in a while, there are no rallies or events on the campaign schedule right now. That's after weeks of counterprogramming with trolling (his word, not just ours) of Democrats by the president as he visited states critical to Democrats' chances to try to draw crowds and attention.

Still, the Trump camp is counting its cash after hitting some big fundraising goals in the last six months: The Republican National Committee's touting $86 million that it brought in last month, plus $60 million more in January.

It's something first daughter and senior White House aide Ivanka Trump touched on in a recent New York Times interview, suggesting that she can out-raise Biden at events: "As an example, she pointed to a rare donor event that she headlined in Houston last November, where she said she raised $2 million in 45 minutes."

And now, Team Trump plans to deploy what it considers its secret weapons — Ivanka and first lady Melania Trump — later this month to raise money more aggressively than at any other point of the campaign.