Michael R. Bloomberg, the billionaire former mayor of New York, was serving tacos and berries to Houston supporters a few days ago. Sen. Elizabeth Warren of Massachusetts rallied 2,100 in Houston and picked up the endorsement of an important national teachers union leader on Saturday. Sen. Bernie Sanders of Vermont attracted thousands to rallies across the Lone Star State, one of the 14 states voting in the March 3 Super Tuesday primaries.

That competition heralds the big shift that will now take place in the Democratic nominating contest, with South Carolina’s primary votes having been counted. The 2020 race has abruptly turned from one-state-at-a-time combat into a national contest. Amassing delegates now is the name of the game.

“You do need to shift from the first four states, where it’s about winning states,” said Lily Adams, who was an advisor to the presidential campaigns of Hillary Clinton in 2016 and Sen. Kamala Harris last year. “In March, it’s about winning delegates, and you have to have a sophisticated strategy about where you are going to deploy your resources.”

California, with its 415 delegates, is the biggest prize on Super Tuesday, but there is little suspense about the outcome: Multiple polls show Sanders as the runaway favorite. The latest UC Berkeley Institute of Governmental Studies poll for The Times found Sanders had a 2-to-1 advantage over his closest rival, Warren.

Delegates are awarded only to candidates who earn 15% of the vote statewide or in individual congressional districts.

Texas, which awards the second largest cache of delegates, 228, has a more fluid, competitive race and will be the first big test of Biden’s ability to refute Bloomberg’s claim to be a better alternative for moderate voters who fear a Sanders victory.

“If you want somebody who has the resources to beat Trump, that’s me,” Bloomberg said in Houston.

Biden’s big victory in South Carolina gives him a much-needed boost. But Biden’s ability to compete in a costly state like this has been limited by his lackluster fundraising, and his organization was thinned to divert staff into early-voting states.

Biden has planned campaign stops in Houston and Dallas on Monday — the first time he’s campaigned in Texas since mid-January, when he went there for fundraisers, according to a candidate tracker maintained by the Dallas Morning News.

Texas — along with other Super Tuesday states such as Virginia and North Carolina — will test whether the momentum Biden will gain from his victory in South Carolina, and the support from African American voters that powered it, will be enough to overcome those disadvantages in money and organization.

Sanders is well positioned in Texas because he has been able to tap into a network of supporters of his 2016 presidential bid — even though he lost the state to Clinton. Sanders held rallies across the state in recent weeks, as his rivals were still campaigning in Nevada and South Carolina.

In a sign of his confidence there and in California, Sanders is stumping this weekend in Massachusetts, aiming to beat Warren in her own backyard — or at least pick up some of her home-state delegates.

Throughout last year, Biden had a solid polling lead in Texas, but it collapsed in January.

“Sanders and Biden are competing for the top two slots as of now, but the field is volatile,” said Jim Henson, director of the Texas Politics Project at the University of Texas in Austin. “With Warren and Bloomberg’s average poll numbers hovering around 15%, in a volatile environment, they are at least in the hunt for delegates.”

The candidates are campaigning at a time of great promise for the Texas Democrats, a party that is growing in a traditionally red state and scored big gains in the 2018 midterm, thanks to the rapid growth of the Latino population and shifting allegiances in suburbs that used to be GOP bastions.

Those demographic shifts play to Sanders’ strength among young urban, Latino populations. Biden aims to draw on the state’s African American voters, older voters and moderates. Warren hopes to run up her numbers in major population centers and college towns like Austin and San Antonio.

Bloomberg has invested more than $53 million in broadcast, cable and radio ads in Texas since entering the race — $10 million in the last week alone — according to the political ad-tracking firm Advertising Analytics. That is nearly nine times more than his nearest ad-spending competitor, Tom Steyer, who dropped out of the race Saturday night.

Sanders has spent $3.8 million on Texas ads. Warren’s and Biden’s spending — $353,000 and $264,000, respectively — is almost trivial in comparison. Pete Buttigieg, former mayor of South Bend, Ind., has spent about $185,000.

The Bloomberg campaign infrastructure — 180 paid staff and 19 field offices around the state — is unmatched by any other candidate. He has traveled to the state six times, with his seventh visit due Sunday in San Antonio.

Recent polls in Texas suggest that Bloomberg’s entry has been damaging to Biden and given Sanders a stronger hand.

A survey of likely Texas Democratic primary voters by Progress Texas/Public Policy Polling found that, with Bloomberg in the field, Biden and Sanders were tied for first place with 24%, followed by Bloomberg at 17%. But when the survey asked voters’ preference if Bloomberg was not an option, Biden led Sanders 31% to 28%.

Bloomberg has won support from potential Biden backers such as Marc Grossberg, a lawyer and novelist who attended the Houston rally.

“At first I thought Biden was the most electable,” said Grossberg, who cast a ballot for Bloomberg in Texas’ early voting. “But that changed as I was watching Biden lose support. You don’t need to be a weatherman to know which way the wind is blowing.”

Even some more liberal voters who preferred other candidates said they were backing Bloomberg because they believed he was the best equipped to beat President Trump.

“Traditionally, I’m a little more liberal, but my main objective is to beat Donald Trump,” said John Pereira, a Houston retiree who asked Bloomberg to autograph a placard during his short walk along the rope line. He gestured to the generous food spread and added, “One thing about Mike Bloomberg is he is first-class. No other candidate will have a buffet bar.”

Warren’s strategy, in Texas and other Super Tuesday states, has been to try to accumulate enough delegates to keep her in the race through the convention, which Democrats increasingly believe will be contested.

“The road to the Democratic nomination is not paved with statewide winner-take-all victories,” said Roger Lau, Warren’s campaign manager in a recent memo to supporters. “This is a district-by-district contest for pledged delegates awarded proportionally.”

Warren has only recently invested in Super Tuesday state ads, including one in Texas that has Julián Castro, a former presidential rival and the former mayor of San Antonio, narrating her career. Her own campaign ad spending has been supplemented by $115,000 in ads bought by Persist PAC, a super PAC supporting Warren. But still the total is dwarfed by the omnipresence of Bloomberg on air.

The Nevada debate — with her withering attacks on Bloomberg — brought a much-needed fundraising windfall for Warren. She raised $9 million in the three days after that debate, according to her campaign, which brought her February total to more than $21 million. In all of January, she’d raised just $10.4 million.

While Bloomberg’s rally was packed with people drawn because they thought he could beat Trump, Warren’s backers were more likely to express a personal connection.

Barbara Bressler, a 69-year-old retiree who had arrived at 4:15 p.m. for the rally, stood at the back of a line of 800 people waiting for photos with Warren. It was 9:45 by the time she got her photo.

“Being a part of the rally was fulfilling,” she said. “I know I early-voted for the right candidate.”