Former Florida governor Jeb Bush pumps his fist as he asks supporters to rally support on his behalf at a campaign event Wednesday in Mount Pleasant, S.C. (Alex Holt/For The Washington Post)

One of the first signs that the presidential campaign had arrived in the wild and woolly political state of South Carolina came Wednesday morning in this coastal retiree haven when Sen. Lindsey O. Graham introduced his favored candidate, Jeb Bush, and issued a warning.

“If you’re not ready to play,” he said, “don’t come to South Carolina.”

A state known for its nasty political brawls is about to host an epic one, pitting a foul-mouthed celebrity billionaire against a band of senators and governors scrapping to challenge him. The Republican presidential candidates arrived here Wednesday ready for 10 days of combat that could bring clarity to what so far has been a muddy nomination contest.

Since Tuesday’s New Hampshire primary failed to deliver much certainty, the Palmetto State’s GOP primary on Feb. 20 could prove determinative for a trio of candidates vying to become the GOP establishment’s consensus alternative to front-runner Donald Trump and Sen. Ted Cruz of Texas.

The attacks began early on Wednesday. Aboard a chartered jet en route to Spartanburg, Sen. Marco Rubio (Fla.) bashed Bush, his one-time mentor, for lacking foreign-policy experience and Trump for not sharing policy specifics. Later in the day, he talked up his opposition to Common Core education standards, an implicit dig at Bush and Ohio Gov. John Kasich, who are proponents.

Meanwhile, Bush and his aides hit Kasich for expanding Medicaid under President Obama’s health-care law and for supporting military defense cuts. “He led the charge to expand Medicaid and is quite proud of that,” said Bush, a former Florida governor. “I wouldn’t be proud of that, to be honest with you.”

Bush also hit Trump, calling him a “phenomenal entertainer” who lacks the temperament to be president.

Katon Dawson, a former state GOP chairman who has not endorsed anyone, explained what makes the South Carolina primary unique.

“People in Iowa expect the candidate to trudge through the snow, do small meetings in diners,” he said. “In New Hampshire, they expect a candidate to come to their living room, sit on the sofa, have some coffee. In South Carolina, 700,000 people want to see how you take a punch.”

Trump sits in the pole position here, where the billionaire mogul’s anti-immigration, outsider crusade has found deep support. Top South Carolina Republicans see Trump as the one to beat, noting that the electorate historically votes based on values and emotion.

Trump rallied a few thousand supporters in a livestock arena at Clemson University in Pendleton, where he went after only one opponent: Bush. Trump called him “low energy” and a “stiff” who is controlled by his donors. “The last thing we need is another Bush,” Trump said as the crowd cheered.

Republican candidate Donald Trump called Common Core "a disaster" at a rally in Pendleton, S.C., on Feb. 10, but then contradicted himself three minutes later. "Common Core, we're going to keep," Trump said. (Reuters)

Trump has about a dozen campaign staffers and four offices in the state, along with three RVs that function as mobile offices in rural areas. But it is unclear whether they can persuade the thousands of people who pack his rallies to cast ballots for him in a primary expected to draw exponentially more voters than the Iowa or New Hampshire contests.

The most consequential moment may be Saturday night’s debate on CBS, where Trump could come under intense fire from Cruz and Bush and where Rubio will seek redemption from a disastrous debate that wounded him in New Hampshire. In 2012, Newt Gingrich’s electric performances in two debates the week before the primary lifted him from a hobbling third place in the polls to a decisive victory over Mitt Romney.

Rubio, coming off a humbling fifth-place finish in New Hampshire, seemed to be in search of catharsis. The candidate accused of being too scripted opened up to reporters aboard his plane for a rare 45-minute news conference.

He drew on his time as a college football cornerback to frame his outlook. “You’re gonna get beat,” Rubio said, adding: “You gotta put that play behind you, because the next play is just as important.”

Rep. Trey Gowdy, one of Rubio’s biggest backers in South Carolina, said the key is to “let people meet Marco.”

“When you meet him, you love him,” Gowdy said. He recalled a recent swing through a Spartanburg restaurant: “By the end of Marco walking around the tables in the restaurant, he was far more popular than anyone he was with. To know him is to love him.”

Two candidates did not make the trip to South Carolina. New Jersey Gov. Chris Christie and former technology executive Carly Fiorina announced Wednesday that they were suspending their campaigns after disappointing finishes in New Hampshire. This leaves six major candidates, including retired neurosurgeon Ben Carson, still in the race.

Trump’s dominance here puts him in the crosshairs of Cruz, who defeated the businessman in the Iowa caucuses after a caustic advertising blitz and attacks on the stump. Cruz plans to replicate that strategy in South Carolina.

“The only way to beat Donald Trump is to highlight the simple truth of his record — it is not conservative,” Cruz said Wednesday in Myrtle Beach.

Cruz was more specific on Mike Gallagher’s talk radio show, highlighting Trump’s past support for abortion rights and bank bailouts.

Cruz is getting backup on the airwaves from his allied super PAC, Keep the Promise I, which has committed more than $2.5 million in the state. Strategist Kellyanne Conway, who runs the group, said the ads would repeat similar attacks leveled against Trump in Iowa.

“There’s some nagging concern he’s gone through the political witness-protection program to emerge a spanking new conservative,” Conway said. “Eminent domain is a big problem for him. If Trump’s entire narrative of ‘I’m for the little guy’ hits a speed bump, it’s because South Carolina becomes more familiar with the victims of Trump’s success.”

Bush is taking a three-pronged approach in South Carolina: Keep up attacks on Trump’s temperament and lack of serious policy ideas; raise doubts about Rubio’s maturity and governing experience; and remind voters in the military-heavy state that Kasich once advocated deep Pentagon spending cuts.

He will be helped by his super PAC, Right to Rise USA, which Wednesday pumped in another $1.7 million in ad dollars on top of roughly $10 million already budgeted. The group is airing one TV ad attacking Rubio’s lack of legislative accomplishments and another featuring an endorsement from former president George W. Bush.

During a Wednesday campaign stop in Bluffton, Bush focused mostly on Trump. When a man asked what he thought of Trump’s vow to run the country like a business, Bush replied, “The problem with Trump is he went bankrupt four times.”

Bush has 20 paid staffers working out of four offices across the state, and his advisers are counting on goodwill for his family name as well as the enthusiastic endorsement of Graham.

Since dropping out of the presidential race, Graham, the state’s senior senator, has quickly become one of Bush’s top strategists. The two have bonded during long car rides and debate prep sessions.

“I’m going to make this a referendum on commander-in-chief,” Graham said. “The centerpiece of my campaign was defending this country, winning a war we couldn’t afford to lose, and the reason I picked Jeb is I think he’s most qualified to do the job.”

Bush plans to make his South Carolina campaign a family affair. He turns 63 on Thursday and is scheduled to make appearances with his wife, three grown children and four grandchildren. He also is expected to campaign with his brother.

“Jeb Bush is bringing in the firepower of 43,” said Dawson, an ally of the former president’s. “If Trump wants to tangle with George W. Bush, that ain’t like tangling with the former governor of Florida. That’s tangling with a Texan, and if the George W. Bush we all know shows up, the one who’s a competitor — well, I relish seeing that fight.”

Potentially standing in Bush’s way is Kasich, who was buoyant following his surprisingly strong second-place finish in New Hampshire. But Kasich is getting a late start in South Carolina, where he has just three full-time staffers. His super PAC, New Day for America, has a robust presence in the state and plans to air ads.

Kasich is targeting moderate voters in specific areas of the state where he can pick up delegates based on South Carolina’s proportional allocation rules, such as Charleston, populated with many business-friendly Republicans, as well as diverse counties in and around Columbia.

Kasich told reporters flying with him to Charleston on Wednesday that he hopes to keep his message optimistic, while acknowledging that the South Carolina dynamic could be dramatically different.

“I know we can’t just go through this, you know, like falling off the turnip truck and saying that everything is just going to be positive, because I’m going to have to respond to some of this stuff,” Kasich said. “But I’m starting to really think we’re on to something.”

Sullivan reported from Spartanburg, S.C., and Rucker reported from Washington. Robert Costa in Manchester, N.H., Jose A. DelReal in Charleston, S.C., Jenna Johnson in Pendleton, S.C., David Weigel in Concord, N.H., and Katie Zezima in Washington contributed to this report.