It was dark and cold, but Bernie Sanders's 5am rally in early February, from the back of a pick-up truck in New Hampshire, stays with the Vermont senator's chief strategist Tad Devine as "a magic moment" of their campaign.

Sanders had just stepped off a plane packed with the American political press corps on an overnight flight from Des Moines, and a razor-thin loss to rival Hillary Clinton, when he spoke to scores of supporters who had waited through the night to greet him.

Watching Sanders speaking on that freezing New Hampshire morning, Devine "felt the Bern. "

"Here's a guy with incredible, boundless energy who just fought Hillary Clinton to a tie in Iowa and was coming into New Hampshire where the polls showed him ahead," said Devine.

“That moment… it really struck me that this thing was possible, that we could find a way to overcome all of the incredible advantages she had as a candidate: the support she had in the party, the resources superiority, the things that made victory look almost impossible.”

For a man considered a long-shot candidate, the result in Iowa was viewed as a victory. It was the first bout in the long fight that Sanders did not concede for another six months.

Now, a month after Clinton was crowned the Democratic nominee at the party's convention in Philadelphia, Devine is in reflective mood on an extraordinary political campaign.

Sanders, the 74-year-old Brooklyn native and self-professed democratic socialist viewed by some as a backbench gadfly in the US senate, became the unlikely energetic alternative to one of the world's best-known politicians.

Electrified the left

His crusade against big money interests in politics and the Wall Street banks, and his support for racial, economic and social equality, a higher minimum wage, free college education and universal healthcare electrified the left wing of the party.

Clinton may be the Democratic presidential nominee but Sanders has shaped the platform on which she now stands because of the campaign he ran.

A curmudgeonly septuagenarian became the improbable poster boy for young progressives at a time when many Americans, angry at the political status quo and frustrated by stalled economic prospects, craved an authentic outsider to shake things up.

"His message of dealing with an economy which favours the wealthy in the United States at the expense of everyone else was very powerful and resonated," said Devine.

Like Barack Obama eight years earlier, Sanders brought a new generation of young voters into the political process.

“He struck a chord with them by his style and manner,” said Devine. “He was blunt and direct and they liked that, and also the ideas that he was talking about.”

This was the seventh presidential campaign that the 61-year-old Democratic consultant has worked on.

He was a senior adviser on Al Gore's 2000 campaign and John Kerry's 2004 campaign, and helped Fianna Fáil at elections over the past 20 years. He would have worked with the party in this year's general election had he not been advising Sanders.

In retrospect, Devine concedes that the Sanders campaign would have been spent resources more quickly, and put staff on the ground a lot earlier. They cautiously held back not knowing if the money pouring in would continue. (It did.)

"We didn't want to get ahead of our skis when we were going downhill so fast," he said. The strategy was to win the first three races in Iowa, New Hampshire and Nevada.

“We had to knock down these dominoes in order for the others to fall and to have a real shot to connect with African-American voters in the South and other voters who knew so little about him,” said Devine.

‘Very aggressive’

When they lost Nevada, the campaign team “huddled” and took a much longer view of the primary with a view to winning it “at the back end,” in

California

in June and other states in the west where the demographics were more favourable for Sanders.

“Until the New York primary, I think we had a very good shot,” he said. Clinton won the state’s primary by a decisive 16-point margin, more than 300,000 votes.

Devine had wanted Sanders to attack Clinton on her emails and the Clinton Foundation – her family charity – but Sanders refused; he thought it too personal.

“The American people are sick and tired of hearing about your damn emails,” Sanders said in the first Democratic debate in October, removing them as a campaign issue.

“I, for one, am somebody who advocated putting everything on the table because you got to do everything to win,” he said.

“This is a tough business. You have to be very aggressive, but Bernie was true to himself and I respect that.”

While some diehard Sanders supporters will never support Clinton, others have switched sides to campaign for her, united by a common adversary in Donald Trump.

Devine believes Trump is failing to pass the very high presidential threshold set by voters “almost on a daily basis”.

If Trump continues trying to excite people on divisive issues such as race and bigotry, he will lose to Clinton by a big margin, Devine predicts.

The trick for the Clinton campaign, he suggests, is to push Trump to defend big, traditional Republican states, such as Texas, so as to force him to spend big on TV advertising, as George W Bush did to Al Gore in California in 2000.

“This is a very tactical campaign,” he said. “If they can force Trump to defend some of these places with large media markets which are very costly and to do something that Trump doesn’t like to do — spend money — the possibility of a landslide victory exists.”

‘Biggest advantage’

Trump is losing right now because Clinton has made this election about Trump, says Devine, but he could have a real shot at winning, if he can “wrap himself around the mantle of change” and establish Clinton as a “status-quo” candidate.

"I saw this in Ireland. It is very hard for anybody anywhere in the world, for any democracy to get a third term of government," he said.

He recalls the 2007 Irish general election and not a single poll or pundit in Ireland saying Bertie Ahern was going to win a third term until the tide turned after the leaders' debate in the last week of the election.

“The bias against a third term exists everywhere,” he said, “and that’s what Hillary Clinton has to confront and that’s Donald Trump’s biggest advantage.”

Devine will speak at the Kennedy Summer School: a festival of Irish-American history, culture and politics in New Ross, Co Wexford, from September 8th to 11th.