Crowds line up to hear Donald Trump at a campaign rally at the Reno Event Center on Jan. 10 in Nevada. (Charles Ommanney/The Washington Post)

— Lindsay Legault-Knowles is the kind of voter the Republican Party is desperate to rouse. She is white and from working-class Vermont. She fears the changes happening all around her. “It’s hard for me to have friends,” she said, “because everyone seems to disagree.”

She drove here on a cold January night to make phone calls on Ted Cruz’s behalf. The presidential candidate’s wife showed up, too. With a silk Hermès scarf draped over her shoulders, Heidi Cruz, a former Goldman Sachs executive, sat down at the campaign office next to the college student, who wore a Confederate flag T-shirt.

They came from different Americas — and never once spoke — but shared a mission: to find more people with backgrounds like Legault-Knowles’s, one call at a time.

Their encounter illustrated the urgent imperative of Republicans — historically the party of business, money and power — to broaden their coalition with many more white working-class voters. As the nation diversifies and the GOP struggles to adapt, the presidential hopefuls see this demographic bloc as the key to taking back the White House.

“Some of them have never voted,” Cruz campaign manager Jeff Roe said. “It’s staggering. If they can be convinced to come out and vote, we win.”

Lindsay Legault-Knowles volunteers at Sen. Ted Cruz’s New Hampshire headquarters on Jan. 6. (Robert Costa/The Washington Post)

There has been a debate within the party — and the political class — about whether Republicans need to diversify to win or whether it just needs to attract more of its core constituencies. So far in 2016, led by Cruz and Donald Trump, the election has moved decisively toward the latter. The exceptions, such as Jeb Bush and Lindsey O. Graham, are either out of the race or on the edges of it.

Trump is making the most visceral, raw appeal to people who feel left out of the economic recovery and ignored by the political establishment. He espouses hard-line views on immigration that border on nativism, protectionist trade policies and a tough approach with countries like China, Japan and Mexico that he portrays as thieves of U.S. manufacturing jobs.

Cruz, a Texas senator, is taking a similar tack, especially on immigration, airing a provocative television ad last week that depicts illegal immigrants racing across the U.S. border in suits and high heels to steal jobs from Americans.

By contrast, Sen. Marco Rubio of Florida is trying to connect with working-class voters through policy ideas. He advocates expanding vocational education and sings the virtues of manual labor. Bush’s aspirational economic message echoes Rubio’s.

Rubio and Ohio Gov. John Kasich also make biographical overtures; the former talks about his unlikely journey as a son of Cuban immigrants, while the latter highlights his upbringing in a hardscrabble Pennsylvania steel town.

“They’re my peeps,” Kasich said of blue-collar voters in a recent interview. “People who think, ‘I get screwed, I get nothing.’ That’s where I grew up. . . . That’s who I am. That’s my DNA.”

Sen. Marco Rubio (R-Fla.) talks about vocational education and manual labor at a town hall meeting Jan. 7 at Nashua Community College in New Hampshire. (Brian Snyder/Reuters)

Yuval Levin, the editor of the conservative National Affairs publication, said the primary “has become a menu of options for the party as it searches for a way to bring them back. One side says we’ll focus on immigration and trade; the other focuses on cost-of-living concerns and market-driven solutions and not so much about culture.”

The mission is not limited to the campaign trail, however. Within the GOP’s congressional ranks, some reform-minded lawmakers, including House Speaker Paul D. Ryan (R-Wis.), are pushing anti-poverty policies. Ryan co-hosted a presidential candidates forum in South Carolina over the weekend devoted to those issues.

Mitt Romney, the GOP’s 2012 presidential nominee, has been encouraging party leaders to develop better policies to address wage stagnation. For instance, he supports raising the federal minimum wage, a departure from Republican orthodoxy.

“As a party we speak a lot about deregulation and tax policy, and you know what? People have been hearing that for 25 years, and they’re getting tired of that message,” Romney said in a recent interview. He added, “I think we’re nuts not to raise the minimum wage. I think, as a party, to say we’re trying to help the middle class of America and the poor and not raise the minimum wage sends exactly the wrong signal.”

Republican strategists describe the party’s relationship with working-class voters as a long flirtation that has veered between an all-out embrace in the years of Ronald Reagan and a drift away in the George W. Bush era.

Whites without college degrees made up 41 percent of the overall electorate in 2012, though that share has declined steadily over the years, according to U.S. Census Bureau data. They made up a core part of Bill Clinton’s coalition in 1992 and 1996 but have moved away from Democrats in recent elections. President Obama lost this bloc by 25 percentage points to GOP nominee Mitt Romney in 2012, the widest margin since Reagan’s 1984 landslide, according to national network exit polls.

As Republicans face difficulties winning over Latino, young and women voters, maximizing support and turnout among working-class whites is critical.

“I think the Republicans are doing this out of necessity,” said Tad Devine, chief strategist for Democratic presidential candidate Bernie Sanders. “They’re being backed into a demographic corner right now.”

On the campaign trail, Trump fashions himself as a prophet for the aggrieved and downtrodden. Last week in Claremont, N.H., he bemoaned the skeletal remains of the region’s once-booming manufacturing economy — and he laid blame on the political leaders of both parties.

“I’m taking our jobs back from China,” Trump exhorted. “You people know better than anybody about jobs leaving an area. Look what happened to you? What the hell? . . . You look throughout New England, it’s still scarred all over the place after many years.”

The night before, he was in Lowell, Mass., sounding his familiar refrain about undocumented immigrants, whom he cast as shadowy villains responsible for sabotaging people’s livelihoods and degrading the country’s pride.

Trump’s campaign manager, Corey Lewandowski, said the candidate’s words for the working class are deliberately personal. “People don’t feel like these jobs have disappeared,” he said. “They’ve been stolen, and they don’t mind if someone is speaking forcefully about taking them back for blue-collar Americans.”

More than anything, Trump’s rhetoric on immigration has captured the attention of working-class whites who say they had been falling away from party politics.

“None of [the candidates] are saying what they should be saying — ‘Get them out of here’ — except Trump,” said Tim Labelle, 73, a retired auto mechanic who voted for Obama in 2008. “They’re taking our jobs, and they’re gonna take over our whole country if we don’t put an end to it.”

Trump claims he has widespread support from unionized workers. But Richard L. Trumka, president of the AFL-CIO, said in an interview that Trump is “trying to confuse them” with “blatant racism.”

“They’re not going to be duped by somebody saying, ‘I know we brought this engineer in for $25,000 when the average wage is $75,000, but don’t worry about that. Worry about this other guy raking your lawn, doing jobs that people normally don’t want that don’t even pay minimum wage,’ ” Trumka said. “He tries to make it seem as if these guys over here really are your enemy.”

Cruz is echoing Trump on immigration, including recently calling for a border wall. In one of his latest ads, titled “Invasion,” businessmen and women stream across the border to show what Cruz calls the “economic calamity” of illegal immigration.

Explaining the strategy, Roe said: “The Republican argument can no longer be just about taxes and spending. It’s got to speak to the working poor and the culture.”

Arthur C. Brooks, president of the American Enterprise Institute, a conservative think tank, said immigration is a useful frame for the underlying issue of the campaign.

“It’s not the issue,” Brooks said. “It’s a reason for explaining the pain being felt by the working class and the working poor, who have tenuous employment and are making $11 to $15 an hour, are not college-educated, and mostly nonreligious.”

Like Cruz and Trump, Rubio has also sought to strike a hard-nosed posture on immigration, distancing himself from failed Senate legislation he co-sponsored that would have provided a path to citizenship for undocumented immigrants. But the tone of his pitch to working-class voters is different.

Addressing a bundled-up crowd last week at a New Hampshire community college’s auto shop, Rubio talked up his plans for paid family leave and a child tax credit. Surrounded by tool boxes, he said that young people need to learn tangible skills.

“What you do here in this center, we need more of,” Rubio said. “We need to be teaching more people to be welders and plumbers and pipe cleaners, auto mechanics and airplane technicians.”

Back at Cruz’s headquarters one night last week, Legault-Knowles and Heidi Cruz were joined by Bob Smith, a former U.S. senator and the campaign’s New Hampshire chairman. While the two women worked the phones, Smith, a towering Vietnam War veteran and former high school teacher, surveyed the room.

“The people we’re all talking to, they are fed up with broken promises,” Smith said. “Republican, Democrat — they’re ordinary working men and women, and they’re not for anyone. They feel like outcasts. And they’re up for grabs.”

Scott Clement in Washington contributed to this report.