The problem is that reality didn’t match the theory.
While some of Sanders’ more conspiratorial supporters will blame the “Democratic establishment” for stealing the nomination from him, the truth is more prosaic.
His voting coalition, while deep, was not broad enough to win the Democratic nomination – except in an over-crowded and fragmented field.
When the race narrowed to a clear two-person choice – Sanders versus Biden – his frontrunner status evaporated.
As he did four years ago against Hillary Clinton, Sanders won big with young Democrats who loved his calls for universal healthcare, free college and legalised marijuana.
This year he also dominated with Hispanic voters, an increasingly important share of the Democratic electorate.
That took him to around a third of the vote, but he couldn’t expand beyond that. African American voters rejected him. So did voters aged over 50. College-educated white voters in the suburbs preferred Biden, as did working class whites.
In 2016, Sanders racked up big victories over Clinton in rural counties where conservative, blue-collar voters dominate.
This time around, voters in the “rust belt” regions of Michigan opted for Biden. This suggests Sanders’ past support among these voters was driven as much by antipathy to Clinton as enthusiasm for his policies.
And while voter turnout has soared in many states, it was older and more moderate Democrats rushing to the polls.
Youth turnout was flat, reflecting the long-standing reality that voters under 35 are the least-likely to show up at the polls. It would have been a massive risk to bet on these voters delivering Sanders victory in November.
And while the Democratic Party’s base is becoming more progressive, it is not as left-wing as Sanders and his supporters would like.
Fifty per cent of Democrats still describe themselves moderate or conservative. A Gallup poll last year showed that most Democrats want their party to move to the centre rather than the left.
The results show that organisation and enthusiasm aren’t everything in politics. Sanders easily drew the biggest and most fired-up crowds to his rallies, and his campaign apparatus was the most impressive.
But voters, no matter how enthused they are, can only vote once. Biden’s rallies have been far more sedate and until recently his campaign was anaemic and underfunded.
But Democratic voters know him, they like him and, most importantly, they believe he has the best chance of defeating Trump in a general election.
Sanders has been hugely influential in recent years moving the Democratic Party to the left. It’s a role he can continue to play in the future, but it won’t be from the White House.
Matthew Knott is North America correspondent for The Sydney Morning Herald and The Age.