HOUSTON — In a packed gymnasium on Saturday, Kamala Harris declared her affinity for Texas. “I love Harris County!” the Californian said of the state’s most populous county.

The same day, Beto O’Rourke was winding down a two-day swing through South Carolina — a state as critical to Harris’ presidential prospects as Texas is to the former congressman’s.

As two of their party’s electrifying and charismatic figures, Harris and O’Rourke have all but ignored the other while running close together in the polls. Yet the early travel in each other’s firewall states — where they were met by rapt audiences — demonstrates the wide-open nature of the 2020 primary and the aggressive steps they’re taking to fortify their standings.

“In a battle for the upstart mantle, it’s a tactical move designed to create momentum for each one while stealing momentum from the other,” said Doug Herman, a Democratic strategist.

Indeed, Harris’ choice to stump in Texas barely a week after O’Rourke announced his candidacy wasn’t by accident: Aides said she wants to make clear that she’s not ceding the Super Tuesday state to O’Rourke or his fellow Texan and 2020 hopeful Julián Castro. She made a stop outside Dallas with a group of county Democrats and visited newly elected black female judges in Houston.

And before a crowd of more than 2,400 people on the campus of Texas Southern University, a historically black college, she pledged the largest-ever federal investment in teacher pay — careful to stress the symbolism of the setting.

“We are not paying our teachers their value,” Harris said, echoing former President Lyndon B. Johnson, a native Texan, who had sought to “bridge the gap between helplessness and hope” when he signed major education legislation of his own in 1965.

Yet if Harris was trying to make inroads on O’Rourke’s turf, he, too, was sending a message in the early days of his bid that he would make a concerted effort to reach black voters whom Harris is aggressively courting. South Carolina is a significant test of a candidate’s ability to appeal to African-American voters — and Harris has made three trips there, hired four staffers in the state and weighed in on local bills to restrict guns and raise teacher pay.

This weekend it was O’Rourke’s turn: On Friday, he rallied a large crowd at South Carolina State University and met with a pair of prominent African-Americans: Willie McLeod, a member of the “Friendship Nine” who fought against segregation in 1961, and Steve Benjamin, the Columbia mayor and president of the U.S. Conference of Mayors.

O’Rourke told reporters in South Carolina that the U.S. must “account for the fact that we have continuing suppression in our economy, in our education system, in our health care system and in our democracy.” And the El Paso native reiterated his support for decriminalizing marijuana and investing in education.

“We are losing out on the potential of everything that every incarcerated man and woman — more likely than not of color — is supposed to do in their time on this planet: the jobs they can work, the families they can raise, the poetry that they are going to compose, the great things that they are going to do in positions of elected leadership and trust,” he said in Rock Hill. “We would be the beneficiaries if we could get this right.”

O’Rourke has outpaced Harris and every other Democrat in first-day fundraising, announcing last week that he had raised $6.1 million from more than 128,000 “unique contributions” in his campaign’s first 24 hours. In an update late Friday, O’Rourke’s campaign said those contributions came from 112,000 individual donors, putting his average donation per person at about $55.

Harris raised $1.5 million from 38,000 donors in her first dayhour period. Her trip to Texas was an obvious warning to O’Rourke, who campaigned in all of its counties in his narrow 2018 loss to Republican Sen. Ted Cruz.

Texas Democrats had become accustomed to — and some times frustrated by — O’Rourke’s reluctance to go negative against Cruz during their Senate race. And while impressing upon his supporters the importance of defeating Trump in 2020, O’Rourke had taken efforts not to personalize his opposition to the president.

“One of the things that hurt Beto so badly in the Senate race is that he just would not make a fist and really attack Cruz to draw a contrast between them,” said Michael B. McPhail, a former member of the Texas Democratic executive committee. “Harris would be the one to really deliver the punches and soften up the Republican opposition.”

But on Saturday, O’Rourke offered a taste of the kind of criticism he is willing to level at Trump. He described the executive branch as “out of control” and said Trump has “maliciously” denigrated immigrants.

“You have a president who, in my opinion, beyond the shadow of a doubt sought to … collude with the Russian government, a foreign power, to undermine and influence our elections,” he said.

Harris, who said she’s being guided by “having a vision of a future in which everyone can see themselves,” continued to lean into comparisons with the president in Texas.

“Let’s start with this,” she said Friday night, bringing hundreds of activists to their feet, “I know, and will know, and do know how to prosecute the case against Donald Trump.”

If Harris was in O’Rourke Country, it wasn’t always evident. Women in the early rows at one event fanned themselves in elation. And thousands filed into a gym at Texas Southern to hear a county commissioner endorse Harris as “a thoughtful prosecutor” who promoted “people who look like me and people who look like you.”

McPhail said it will be difficult for Harris and other out-of-state candidates to surpass O’Rourke in his state. But as he waited to see Harris for the first time, he hoped to see her on the ticket, either leading or accompanying O’Rourke as the vice presidential nominee.

“They’re like the velvet glove and the iron fist,” he said.