Sen. Lindsey Graham speaks about Yemen on March 26. (Win Mcnamee/Getty Images)

Lindsey Graham spoke in his measured, mellow tenor as he stood recently in the sanctuary of a historic synagogue, reflecting on Iran and Israel, radical Islam, Nazis, and, of course, President Obama’s foreign policy.

“We know how this movie ends unless good people rise up and stop it before it’s too late,” he said.

Graham, the senior senator from South Carolina, is one of the many, many Republicans exploring a 2016 run for the White House. As Graham sees it, as a foreign policy expert and colonel in the Air Force Reserve, he adds a critical ingredient to the sprawling field — the credentials to lead the charge against the Rand Paul wing of the Republican Party.

Sen. Paul (R-Ky.) announced his White House bid this past week by positioning himself as a critic of U.S. domestic spying and nation-building abroad — giving Graham an opening.

The primaries will be “a fight within the party between isolationists, libertarians and people like myself who represent a more traditional view toward national security,” he said in an interview.

Sen. Lindsey Graham speaks during the Iowa Ag Summit March 7. (Daniel Acker/Bloomberg)

“Libertarianism,” he scoffed, “is to the left of Barack Obama.”

On Thursday in New Hampshire, the spring break destination for hopeful candidates, Graham stressed, “I don’t believe, quite frankly, that Paul’s politics on foreign policy are a whole lot different than Obama.”

Yet so far, while Paul and other top-tier contenders have begun to build national followings, Graham’s potential candidacy has gained little traction.

He doesn’t seem to enjoy an advantage of coming from a state with a crucial early primary that might give a boost to a favorite son. One recent straw poll in his home state did not include Graham on a list of 25 potential candidates. And when he is mentioned, a presidential bid lacks support: Almost two-thirds of surveyed South Carolina voters disapproved of Graham seeking higher office.

Part of Graham’s challenge is that he does not fit the candidate mold in an era of high-def visuals, crusading rhetoric and constant buzz.

His approach to legislating — stepping out as one of the few Republicans to support attorney general nominee Loretta Lynch and as a serial bipartisan negotiator on issues such as immigration, global warming and the use of the Senate filibuster — is seen by many GOP activists as apostasy.

Sen. Lindsey Graham speaks on security threats at the U.S. Capitol on March 12. (Mandel Ngan/AFP/Getty Images)

“Immigration is a national problem that can’t be solved by one party,” said Graham, who turns 60 in July. “I believe climate change is a real problem made by man-made activity. The solutions are where the fights should be.”

Graham said he understands the uphill battle.

“For anybody to run for president, you got to take a risk, you got to stretch yourself, the personal hell you have to go through, I realize all that,” he said.

Graham has repeatedly visited Iowa, as well as New Hampshire, where Sen. Kelly Ayotte (R) is a close ally. He has begun courting donors aggressively in the monied quarters of Connecticut and New York — and raising funds for his new political action committee, Security Through Strength. He plans to make an announcement by late May.

On the day Israeli Prime Minister Benjamin Netanyahu addressed Congress last month, Graham’s PAC held a luncheon fundraiser co-chaired by casino mogul and GOP mega-donor Sheldon Adelson and his wife, Miriam, along with other wealthy party supporters of Israel. The event served as an early indicator of where Graham sees his financial base as a pro-interventionist candidate.

In some ways, Graham seems most animated by the prospect of directly challenging Paul. The senator from Kentucky has recently embraced more hawkish views but still criticizes GOP neo-
conservatives for pushing the United States to intervene too often around the world. In separate television interviews this week, Graham accused Paul of being weak on Iran, while Paul charged that “almost anyone in the Congress would better defend the Bill of Rights than this particular senator,” referring to Graham.

The South Carolinian said he began mulling a presidential run moments after winning a third Senate term in November — though his closest political ally and mentor, Sen. John McCain (R-Ariz.), conceded that “we’ve been talking about it for years.”

Graham, McCain and a trusted circle of advisers are betting heavily that national security will rank as a top issue among voters and that the senator’s skills as a prosecutor and debater will offset the deficits.

In more than two decades in politics, Graham has never lost a race, moving from the state house to the U.S. House after one term. He quickly rose to prominence by challenging Speaker Newt Gingrich’s leadership while assuming a prominent role in Bill Clinton’s impeachment. (Graham notably quipped, “Is this Watergate or ‘Peyton Place?’ ”)

Last fall, he bested six primary opponents who challenged him from the right, deriding the immigration bill the senator helped author that would have put illegal immigrants on a citizenship path as “Grahamnesty.”

As for a presidential bid, “I looked at what I have to offer and said, ‘Okay, there’s going to be a lane available on national security,’ ” he said. Graham also looked at South Carolina’s status as the first-in-the-South primary and asked, “Why not?”

Over a dinner of fried green tomatoes and pan-fried chicken livers at his favorite restaurant, Magnolia’s — Graham rarely deviates in gustatory matters — he praised the potential 2016 field.

Sen. Marco Rubio “will be president one day, whether it’s 2016, I don’t know.” Jeb Bush “couldn’t be a nicer guy, very humble, very smart.” Even the junior senator from Kentucky: “I like Rand Paul. We’ve done several things together. I just don’t agree with his foreign policy.”

Graham surrounds himself with a loyal, long-serving coterie of supporters and staff, many of whom address him by his first name, a surrogate family for the lifelong bachelor whose technological deficiencies (he dictates ­e-mail) are matched only by his domestic skills, the refrigerator of his Capitol Hill townhouse a repository of diet soft drinks and antique condiments.

They’re true believers, along with McCain, 78, who famously beat George W. Bush in the 2000 New Hampshire primary and became the GOP nominee in 2008. McCain recently referred to Graham as his “illegitimate son.” Of McCain’s role in a possible campaign, Graham said: “We’re going to have to tie John up. He’ll be in New Hampshire more than I will.”

It’s unclear how Graham — a pronounced Luddite who carries not one flip phone but two — will function as a national candidate in the age of social media. It’s impossible to imagine Graham appearing, as Paul recently did, in jeans talking tech at South by Southwest. He doesn’t wear jeans. He doesn’t do tech. Graham said he intends to win over GOP voters who believe in a less confrontational approach to politics — or, as he calls it, the “problem-solving nature of conservatism.”

But, even in South Carolina, some party leaders are turning to potential political rivals. Previous state GOP chairman Katon Dawson is supporting former Texas governor Rick Perry. “Lindsey has a tremendous amount of Washington legislative experience, and Rick has executive experience,” Dawson said.

“This has always been a business to me. We make business decisions,” Graham said. “I am conservative by any rational definition, fiscally and socially, but I don’t mind embracing problem-solving.”

That “practical view toward issues,” he said, led him to be the lone Republican on the Senate Judiciary Committee to approve the Supreme Court nominations of Sonia Sotomayor and Elena Kagan. “For us to get our judges, we’re going to have to give them theirs,” he said.

Should Graham run, he will no doubt introduce voters to his colorful beginnings, a childhood where pool, not politics, played a prominent role.

Where Graham comes from is Central, a two-stoplight town that, contrary to the name, is tucked in the northwest corner of the state, in the shadow of Clemson. Millie and F.J. Graham — Florence James, though everyone called him Dude — owned the Sanitary Cafe, a hamburger house, bar and a pool hall with three tables in the basement. Dude also ran a liquor store. “We all lived in one room in the back. No shower,” Graham said. “Took a bath in a big iron washtub.”

As a teenager, Graham helped run the pool hall on weekends when gamblers working the Southern circuit, hustlers with sobriquets like One-Eyed Jack and Crooked Stick, would migrate to Central.

“You can’t gamble in South Carolina, so at midnight, we would lock the pool room,” Graham said. This posed no problem with the police chief, a frequent guest. “I would rack the balls, and there would be as many people as we could get in that basement watching. We’d have 100 or more people easy, sitting everywhere,” Graham recalled. “These guys would play pool until sunup. My mom would cook hamburgers all night. They would put $100 bills in all the six pockets. I’ve seen car titles pass. These guys taught me to shoot pool. They could make a cue ball talk.”

Graham was a fabulously indifferent student. Yearbook superlatives eluded him. He was interested in sports, yet he was scrawny, more determined than talented.

Graham was the first person in his family to graduate from high school and college. He claims to have barely broken 800 on the SATs. In law school, he finished near the top of his class.

When Graham was an undergraduate at the University of South Carolina, his parents died 15 months apart. He sister Darline was 13. The family lost its business. An aunt and uncle took her in and loaned Graham money, but he viewed Darline as his charge, returning every weekend, offering to quit school, and ultimately adopting her after enlisting in the Air Force so she would enjoy his benefits.

This is the crucible in the Graham biography that, by all accounts, defines him. It is the reason, friends cite, that Graham became driven and has remained single.

“He had it rough. He assumed responsibilities that he didn’t have to assume,” said Bob McAllister, a political adviser.

His sister, Darline Graham Nordone, now public information director for the state’s Department of Vocational Rehabilitation, described him as a “workaholic.”

“If he had a wife and family, he would really be torn,” she said. “He wouldn’t want to sacrifice his family’s happiness for the job.” She added, “I’ve always had him, but who did he have? Breaks my heart.”

Her brother adopts a pragmatic approach. “You just wake up one day and you’re 60 years old. That’s just the way life is,” Graham said.

“You can think of a million reasons not to go forward,” he said. “If we can find a pathway forward, we’ll take that risk.”

Graham was already working on his elevator speech: “Build up people. Kill the terrorists. Do retirement reform. Create a good, strong energy environmental policy. Call it a day.”

Special correspondent Paul Steinhauser in New Hampshire contributed to this report.