Ben Carson addresses supporters at a campaign rally Thursday in Mobile, Ala. He and other Republican presidential candidates are organizing across the South in preparation for Super Tuesday. (Mike Kittrell/AP)

Ben Carson journeyed here last week to the buckle of the Bible Belt, where he proclaimed the United States a “Judeo-Christian nation” and delivered a stern warning to his devoted followers: Show up at the polls March 1 or face consequences.

On Saturday, Donald Trump again swooped into Alabama, where he has cultivated friendships with immigration hard-
liners, to rally fans in Birmingham. Sen. Marco Rubio (Fla.) has his eyes on the state, too, recently becoming one of only two candidates (Carson is the other) to submit a full slate of 76 delegates for its primary.

Then there’s Sen. Ted Cruz (Tex.), whose volunteers have been buzzing around Alabama gathering names of grass-roots opponents of the Common Core education standards. At next weekend’s Alabama-Auburn foot­ball game, Cruz’s campaign bus will be parked with free stickers and literature. “The Iron Bowl is a big, big moment in Alabama, and Cruz people will be everywhere,” said Ann Eubank, the senator’s state co-chair.

Alabama has become an unusual magnet for Republican presidential candidates because it is one of 11 mostly Southern states holding primaries or caucuses on March 1 — the delegate bonanza known as Super Tuesday.

While the February states — Iowa, New Hampshire, South Carolina and Nevada — are expected to set the tone and winnow the field, Super Tuesday will arrive like a thunderclap, probably determining which candidates will survive for what could be a protracted battle for the nomination.

Ted Cruz launched his presidential campaign in Virginia, one of 11 states with contests on March 1, Super Tuesday. He is pictured with his family on stage at Liberty University in Lynchburg. (Matt McClain/The Washington Post)

“It’s a huge delegate haul, and it’s either going to change the momentum coming out of the early states or reaffirm it,” said John Weaver, chief strategist for Ohio Gov. John Kasich, who is building an Alabama coalition led by the state’s governor.

For centrist Republicans such as Kasich, the aim may not be so much sweeping Super Tuesday as surviving it. After March 1, the calendar turns more to their liking, with a number of winner-take-all states in less-conservative regions where suburban, business-friendly Republicans may matter more than evangelicals and tea party activists.

For Trump and Carson, the political outsiders who have dominated the race for months, Super Tuesday has long been seen by party operatives as the turning point when one of them could surge.

For Cruz, who has sought to appeal to many of the same voters as Trump and Carson, the Southern states are essential. He sees them as his best chance to leap ahead of his rivals after what could be a muddled field by late February. In Georgia, for instance, he has enlisted more than 100 county organizers and has volunteer chairmen in all 14 congressional districts. His wife, Heidi, visited the Atlanta suburbs last week to talk up her husband’s candidacy to Republican women.

Cruz campaign manager Jeff Roe said: “Our approach is to have neighbors call neighbors, pro-lifer to pro-lifer, gun owner to gun owner. That philosophy is painted on our wall — to personalize each contact so that it’s not somebody calling from a remote-access phone bank in another state with a neutral dialect.”

Super Tuesday has taken on the nickname “the SEC primary,” a reference to college football’s Southeastern Conference, because of the many Southern states at play: Alabama, Arkansas, Georgia, Oklahoma, Tennessee, Texas and Virginia.

Republican presidential candidate Donald Trump gestures to the cameras while greeting supporters at a campaign rally last week in Worcester, Mass. Massachusetts is another Super Tuesday state. (Brian Snyder/Reuters)

But other March 1 contests will test the candidates in different ways, such as primaries in Massachusetts and Vermont, two states where Republicans are marginalized but that feature strong conservative currents. Minnesota has caucuses that reward field organizing, while Alaska is so remote that few candidates have campaigned there.

Securing the nomination is a matter of accumulating delegates, and exponentially more are up for grabs on March 1 — 595 total — than in the four early-voting states, which together have 133 delegates, according to figures provided by the Republican National Committee.

Super Tuesday delegates will be awarded proportionally, many of them by congressional district. This gives lower-tier candidates opportunities to pick up delegates without winning the states outright, so long as their vote totals meet the minimum thresholds, which vary by state from 5 percent to 20 percent.

“Everyone feels like they can come in and leave with a few delegates, so we see an uptick in campaigning and organizing over the past few cycles,” said Brent Leatherwood, executive director of the Tennessee Republican Party.

Consider former Arkansas governor Mike Huckabee, who is struggling nationally but hopes to win delegates by overperforming in the March 1 Southern states, many of which he carried in 2008.

“We’re focused on where we can get the most delegates, the biggest bang for the buck,” strategist Chip Saltsman said. “For example, in Texas, there are some rural congressional districts where if you go do a visit, you might pick up more voters than if you were up on Dallas TV for a week.”

Sen. Rand Paul (Ky.) also is vying for Texas — which his father, Ron, represented in Congress — but is concentrating on turning out young voters there and in other Southern states to pick up delegates. Campaign manager Chip Englander said that Texas is “proportional, and it has a lot of college towns, so we have Ron’s supporters with us and lots of college students.”

Carson’s playbook in Texas is similar to that in other Southern states — targeting majority-African-American congressional districts to win delegates.

“Dr. Carson is already a legend in these communities,” said Barry Bennett, Carson’s campaign manager. “So we’re going to churches, to community centers where, frankly, most of the others don’t go.”

The surgical approach to Super Tuesday extends to the airwaves.

Bennett said: “Our voters aren’t only watching ‘Jeopardy’ or the evening news. ‘Friends’ reruns, actually, do very well for us, and that isn’t a typical buy. Our audience tends to be a few more percentage points women than men, so we’ve recently done less ESPN and more Lifetime.”

Jeb Bush’s allied super PAC, Right to Rise, has booked $14.5 million in television advertising in March 1 states and plans to spend at least $2 million more. The ad reservations offer clues about the former Florida governor’s strategy.

Right to Rise is spending heavily in Texas, home to former presidents George H.W. Bush and George W. Bush, as well as Georgia, Tennessee and Virginia, where there are suburban districts with relatively moderate Republican electorates. But it has not reserved any time in Alabama or Arkansas, which are ruby-red conservative bastions.

The Bush campaign acknowledges that he is unlikely to win by towering margins across the Southern states, but advisers intend to maximize his performance in specific areas.

“We’re being very efficient with our spending,” said David James, Bush’s national political director. “There’s an algorithm we’ve developed to maximize our candidate and our time.”

Trump’s operation has been putting him in front of raucous crowds in red and blue states, and he has been making frequent trips to Massachusetts, Tennessee, Texas and Virginia, as well as Alabama, where in August he had one of his first mega-rallies in Mobile.

Campaign manager Corey Lewandowski is in touch daily with organizers in the Super Tuesday states and readily rattles off statistics showing progress: 11,000 people through Secret Service magnetometers Nov. 16 in Knoxville, Tenn.; 16,000 petitions (more than three times the required number) submitted to get on the ballot in Virginia.

“Mr. Trump is sophisticated when it comes to understanding the importance of the calendar and what comes after the first few states,” Lewandowski said. “That’s why he wants to keep going back to Massachusetts, back to Alabama.”

Trump aspires to knit together coalitions of disaffected blue-collar voters and “Reagan Democrats” in places like the Houston area or in western Massachusetts, where more than 10,000 people showed up at his boisterous rally in Worcester last week.

As Trump fans zig-zagged through the security line, volunteers with clipboards gathered signatures on a petition to get Trump onto the Massachusetts ballot. At a long table, seven young men in dark blazers collected contact information from each attendee. Then came another table with more petitions for those who snuck past the clipboard crew.

Alex Perch, 30, arrived three hours early for the Worcester rally, wearing a camouflage hat embroidered with Trump’s “Make America Great Again” slogan and carrying a copy of the mogul’s latest book.

“It’s so weird,” Perch said of Trump campaigning in Massachusetts, the launching pad of more establishment candidates such as the 2012 GOP nominee, Mitt Romney. But, he said: “Donald is doing unbelievable in Massachusetts. He thinks he has a shot at taking Massachusetts. . . . If the moons on Jupiter align and this happens, it’s going to be wild.”

Costa reported from Washington. Jenna Johnson in Worcester, Mass., contributed to this report.