As Joe Biden was on stage in Los Angeles declaring a big Super Tuesday win, his speech was interrupted by screams and scuffles as two figures broke through the crowd and the Secret Service, leaping onto the platform beside him.

In the age of Islamic State and mass shootings, it was an unnerving few seconds for those of us watching on.

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In fact, they were just protesters, trying to convince Americans that drinking milk is an act of animal cruelty.

An image of the former vice-president's wife Jill Biden throwing herself between the angry vegans and her husband went viral.

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Then Biden got on with his speech, apparently unfazed.

It was emblematic of the way his campaign has unfolded.

A man, apparently in grave danger of being pushed off stage, was saved at the last moment thanks to the ferocity and determination of those around him.

Biden is now the favourite to win the presidential nomination.

Sanders looked poised to steal Biden's spot

Two months ago, a prediction that Biden would get the nomination would have been a safe take.

"Let's go on to the White House," Bernie Sanders told supporters at a rally in his home state, Vermont. ( Reuters: Jonathan Ernst )

Polling showed him in the top spot, and his fundraising numbers remained steady.

But by the end of January, Biden's situation appeared dire.

Evidently doubting his viability as a candidate, Mike Bloomberg swooped into the race after months of insisting he didn't want to steal Biden's thunder.

The former New York mayor spent hundreds of millions of dollars to try to beat Trump.

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With the moderate vote starting to fracture, Bernie Sanders emerged as the clear progressive choice.

Biden's spot as the field's frontrunner seemed all but gone after Sanders seized sizable victories in the first three contests: Iowa, New Hampshire and Nevada.

As the South Carolina primary approached, the media ran headlines like "Joe Biden's Last Stand".

But the Sanders campaign would have felt a pang of worry when they saw Biden securing a steady lead in the polls ahead of the contest there.

Sanders swiftly turned his attention to the next prize up for grabs, skipping the final rally in South Carolina to start campaigning in Super Tuesday's greener pastures.

The trouble is, South Carolina wouldn't be a quick race long forgotten because Biden didn't win South Carolina by a small margin or even a comfortable one.

He swept the state by almost 4 to 1, a performance so strong that the US media declared him the winner within five minutes of the polls closing and only 1 per cent of the votes tallied.

Pete Buttigieg threw his support behind Joe Biden after dropping out of the presidential race. ( Reuters: Elizabeth Frantz )

It was enough to inspire two key moderates — Amy Klobuchar and Pete Buttigieg — to bow out of the race and throw their support behind the former vice-president.

And that sparked key endorsements from other Democratic party bigwigs, including former candidate Beto O'Rourke and former Senator Harry Reid.

Four days after South Carolina started voting, Biden again had the news cycle, the money and the frontrunner's momentum.

Then along came Super Tuesday

From the very first results, it was clear that Sanders had lost his edge.

Biden took Virginia with 53 per cent of the vote, a state where he was polling five points behind Bernie Sanders four days earlier.

Joe Biden's victory in South Carolina appears to have given him momentum with voters going into Super Tuesday. ( Reuters: Elizabeth Frantz )

Then Biden won in Southern states like Alabama, North Carolina, Tennessee and Oklahoma. And he won in Northern states like Massachusetts and Minnesota.

He defied all expectations by winning in Texas, a state with a heavily Latino population, where Sanders had been predicted to net the delegate-rich state.

In the end, Sanders only won in Vermont, Utah, Colorado and California.

Though Biden is still a long way from the 1,991 delegates needed to reach the nomination, he's easily leading Sanders in the count.

The road to the nomination looks set for Biden

It may take a few days for the full narrative to form, but things are only going to get harder for the Senator from Vermont.

Bernie Sanders needs strong youth support to win the Democratic nomination, but they failed to vote for him in high enough numbers on Super Tuesday. ( Reuters: Mike Segar )

Sanders's only reliable pathway to the nomination was to sew up the majority of delegates before arriving at the convention in July, thus avoiding the likely prospect that the prize would slip through his fingers in the second round of voting there.

Without another major game-changing performance, it's hard to see such a majority materialising for Sanders.

Exit polls revealed that voters made up their minds at the last minute, which suggests the contests going forward will be even more challenging for Sanders.

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The African American electorate, which puts a premium on electability, showed up in solid numbers for Biden.

Younger voters, who tend to back Sanders, stayed home.

And just like in South Carolina, Biden's win was so clear that it inspired a key candidate to drop out and endorse him.

Mike Bloomberg won only American Samoa, despite spending more than $750 million on political advertising. ( Reuters: Maria Alejandra Cardona )

Mike Bloomberg's exit comes with an extra boon for Biden: money.

The former mayor has always said he'll invest whatever millions or billions are needed to beat Trump.

He'll now write his cheques for Biden.

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Granted, there are still more than 100 days until the nominating convention.

There are still 39 races on the docket and 60 per cent of the delegates to be awarded.

Maybe Sanders will somehow recapture the magic of late January.

Or maybe, like the vegan protesters who stormed Biden's stage, Sanders provided no real threat after all.