Oxford, England (CNN) Few people will ever cast a vote for their younger brother in a presidential primary. Larry Sanders has done it twice.

"It's a rare treat," Bernie Sanders' elder brother tells CNN after voting in Super Tuesday 's Democrats Abroad primary, near his home in Oxford, England. "When I got to color in the box, I colored it in very heavily."

"There's a chance that he'll win -- which is just astonishing," Larry adds, his low, gravelly tone of voice and unpredictable hand gestures matching those of his brother. There are 17 delegates up for grabs in the ongoing Democrats Abroad primary.

Millions of voters across the Atlantic also entered polling stations on Tuesday, sweeping Joe Biden to a series of stunning victories that forced Mike Bloomberg and Elizabeth Warren from the field and reshaped the contest into a two-horse race.

But the elder Sanders, who woke up at six in the morning on Wednesday to follow the night's results live, is unwavering in his optimism for his brother.

"In my view, he is going to be the Democratic nominee," the 84-year-old says as the final ballots were counted, pride still shimmering from his voice. "An obscure politician from an obscure state is taking on all the elites in the Democratic Party -- and at the moment, it's a stand-off."

CNN spent Super Tuesday with Larry, who is leading his own intensive campaign in his adoptive country to secure expat support for the man he still calls "Bernard."

It's a small but affectionate contribution to the "political revolution" that the firebrand candidate has promised will carry him to the White House -- and an interruption to the comparatively obscure life Larry leads in a leafy English suburb.

In a day that mirrors Bernie's own diary, Larry -- himself a long-serving local politician in England -- spoke to hordes of media, posed for photos with adoring fans, took a train to London and made a roaring speech at a Bernie Sanders rally.

He also shared his concerns about his brother's safety, his dim view of his primary adversaries, and his particularly unflattering thoughts on Donald Trump -- the man waiting for whoever emerges from the Democratic contest.

Larry's most staunch position, though, was his defense of his younger sibling. He warns against a Biden nomination, calling the former vice president "a symbol of people who don't really care very much."

"I think Bernard is Trump's nightmare," Larry says.

'It's like walking with a rock star'

Physical resemblances aside, evidence of Larry's family connection is subtle; a "Bernie" sticker adorns the door of his refrigerator, and a poster from 2016 hangs among piles of books in his living room, but Larry's home otherwise resembles any other on his picturesque residential street.

The academic and UK Green Party politician -- currently the party's spokesperson for health -- moved to the UK in 1968 and became a social worker, but returns to the US intermittently and holds dual citizenship. Larry has also run for Parliament a handful of times.

An activist watches Larry Sanders at the Democrats Abroad primary in Oxford, England.

Though he claims partial credit for a few of Sanders' health care proposals , politics is rarely discussed. "He knows I follow politics and he's not interested in talking about it, because he's living it all the time. So we don't really talk politics," Larry says. "He turns it off ... I think it's been very important for him to come down and touch base" during their conversations, he adds.

The two brothers used to speak on the phone every Sunday, but the demands of a presidential campaign have made those calls less frequent. They last spoke three weeks earlier, discussing how Bernie was coping following the sudden death of his daughter-in-law, Raine Riggs.

Still, the brotherly bond is strong. "His house is bigger, and he's doing different things day-to-day, but in fact our way of life -- what we value -- are not dissimilar."

Those values were crafted in the 1950s and '60s, when the two Sanders boys were growing up in Brooklyn, New York.

"Bernard wasn't particularly strong and not much of a fighter, but he was an athlete so he could handle himself," Larry says, recalling a time when his brother, about 10 years old, confronted a group of boys who had bullied his friend.

"One of his friends came up to me the next day and said, 'I have to tell you -- your brother is really a very good guy,'" he says. "He was very respected."

A sense of danger was never far from the Sanders; when Bernie was an infant, much of their father's family was killed in the Holocaust. "We understood that these people had been killed, and if we'd been there we would have been killed," says Larry. "There was a sense that this is not a very safe world."

Now, he rarely worries about his brother's health; "he's healthy, he's fit, he feels better now than he did before the operation," that he underwent following his sudden heart attack late last year.

But he is acutely aware that Bernie's rapidly elevated profile has earned him detractors.

"I do worry there are a lot of lunatics with guns in America," Larry says. "That's been a fear of mine from the first campaign on ... there are a lot of people who hate him.

"Because I'm watching him a lot and he's covered so heavily, the odds are I'll hear from the television or online if something terrible happens, rather than from his wife," he adds, vocalizing a scenario that has evidently occupied his thoughts. "It is very difficult to absorb."

Larry Sanders at his home in Oxford.

But Larry's initial feeling about his brother's success is one of pride. "I remember those first big rallies when he's suddenly jumping up onto a stage," Larry says, discussing a visit he paid Bernie during the 2016 campaign. "That was mind-blowing -- the size, the enthusiasm. It's like walking with a rock star."

Larry nonetheless keeps his sibling grounded. "People around him probably think I'm a little disrespectful -- they want to tell him what they want him to hear, they're his advisers, but I think they think I interrupt him more than he should be interrupted."

A Sanders presidency

Larry recites polling averages, demographic breakdowns and statewide studies with an ease that even the most seasoned politico would envy -- and it's clear his attention is almost permanently locked to his brother's fortunes.

"It's clear to me that he's in there with a chance. It's also clear to me that it's not a certainty," he says, calling a potential Sanders presidency "world-changing."

He doesn't heap the same praise on the "mediocre" Biden, whose dramatic comeback on Super Tuesday helped put him back in contention with the left-wing senator.

"He comes across as a nice guy ... but he's got very little ambition," Larry says of Biden. "He's a heart and soul member of the 'we can't really do very much' campaign."

Bernie Sanders (right) as a toddler with his brother Larry.

He also offers some defense of his brother's controversial comments praising Cuban social programs . "Castro's Cuba did do good things for people. Bernard has never for one moment thought it was a good place to live, because he doesn't like to live in a totalitarian society," Larry says. "But the fact that people lived longer is worth noting."

Larry contests reports of a harassing "Bernie bro" culture among some of his brother's online supporters. "I don't see any evidence whatever for that," he says. "I am definitely not a Bernie bro." Bernie Sanders, for his part, has condemned that behavior among a subset of his supporters.

Larry adds there is little that can be brought up by Biden or Trump that would turn voters against Sanders.

"There are several articles he wrote that seem strange, which (Trump's campaign) will recycle," he admits. "(But) I think there are three guys in the outback in Alaska who don't know that Bernard's a socialist. So what are they going to say?"

Bernie Sanders describes himself as a democratic socialist , though Larry is less precise in using the "democratic" prefix. "Because I'm stupid -- I'm not as good a politician," he says with a laugh, when asked to explain why. He then clarifies that Bernie is "by no means an authoritarian."

"Most people would recognize that he's sincere and decent," he adds. "They may think his ideas are crazy."

'He knew Clinton was struggling'

Larry's more immediate concern is the Democratic candidates Sanders has seen off, and the one he still must face.

"I think all the candidates, with the possible exception of (Elizabeth) Warren, are basically right-wing candidates," Larry says. "(Mike) Bloomberg was a poor mayor" of New York, he goes on, while Pete Buttigieg and Amy Klobuchar were destined to eventually withdraw, he believes. On Wednesday, Bloomberg also pulled out and backed Biden.

Larry's level of disappointment with the rest of the field is shared by many Sanders supporters, leading to questions over how many would flock to a different nominee in a general election. An Emerson poll suggested just 53% of Sanders voters would definitely back the nominee if it is not him, compared to 72% of total Democratic voters.

"Bernard would certainly support the nominee," Larry says when pressed on whether Biden would get support from the Sanders camp if he wins the nomination. "I don't know, I would be very unhappy," to do the same, he adds. "Against Trump? Yes, I would vote for Biden," he eventually concludes, with a sigh.

Sanders also supported Hillary Clinton, a critic of the senator long since their 2016 battle for the Democratic presidential nomination ended, when she went on to face Trump that November.

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That year, Larry made an emotional speech in front of his smiling brother at the Democratic National Convention, before casting a roll call vote for Sanders in the Democrats Abroad primary.

"When your brother is in that kind of position and so many eyes are on him, and he's done such an amazing thing, I did think of our parents," Larry says. "They had a hard life, they died young -- they never saw Bernard's success and they would have been immensely proud," he adds, trying and failing to fight back tears. "It still chokes me up."

But months later, Trump stormed to a pundit-defying victory. "He was devastated," Larry says, recalling his first conversation with Bernie after that general election. "He thought it would be a terrible time for the people."

"I think he was frustrated," Sanders adds. "He was concerned -- he didn't think (Clinton) was a strong candidate ... he knew she was struggling, but he thought she would win."

On the current President, Larry is unabashed. "Neither Bernard or I are alone in this: he's an incredibly frightening person.

"His responses to international events are so chaotic, stupid, uninformed," Larry adds, increasing in indignation with each new adjective. "He deals with international events, in my opinion, like a stupid child."

But he sees some political similarities between the two men. "Bernard shares that anger against the system -- the difference is he's got actual, real things to do about it."

A campaign stop in London

Hours later, Larry leads a Sanders rally outside the UK Parliament in London. This time, he's the rock star; fans hoisting "Bernie" placards stop to take a picture with Larry, cheering his name and listening intently to his mobilizing speech.

The event draws a healthy crowd of expat voters, and a few Britons still stung by December's decisive electoral loss of Labour leader Jeremy Corbyn -- who had garnered comparisons to Sanders.

"If we want to have progressivism in the world, it has to start in America," Amen Tesfay, who attended the rally, tells CNN. "Despite him being an American, (Bernie's) ideas are what we look forward to ... if he's able to mobilize America, the whole world can start to move forward," adds Maria Garcia, who recently moved to London from Spain.

'Bernie Abroad' badges at an English Sanders rally.

Whether the first part of that equation becomes reality remains to be seen; as Biden and Sanders move towards the remainder of the primary calendar, the race is painstakingly close.

But to Larry and the scores of like-minded attendees, Sanders' success -- regardless of where he ends up -- is an achievement in itself.

"It's amazing, if you stop to think about it -- the larger part of the Democratic Party is waged against him, and it's pretty even," Larry says. "I'm very proud. And I also think he's right, which helps."