Joe Biden’s surprise victories on Super Tuesday were powered by Democratic voters who broke his way just days before casting their ballots — a wave of late momentum that scrambled the race in a matter of hours.
The late deciders helped Mr Biden win Massachusetts, Minnesota, North Carolina, Texas and Virginia, among several other states.
In some states, they made up roughly half of all voters, according to AP VoteCast surveys of voters in eight state primaries.
And the surveys show they lined up behind the former vice president.
In Virginia, where nearly half of the voters waited to make up their minds, Mr Biden won two-thirds of the late deciders.
The surveys show the power of a well-timed surge in a race that has been defined by a crowd of candidates and confused voters agonising over the best challenger to President Donald Trump in November.
Mr Biden’s big win in South Carolina on Saturday revived his struggling campaign and within 72 hours pushed three of his rivals toward the exit and swung the opinions of voters in distant states.
Yet Vermont Senator Bernie Sanders found a way to blunt the impact.
By organising aggressively and banking early votes from his liberal, young and Latino coalition, Mr Sanders won Colorado and California.
About 80% of Sanders voters in California said they picked their candidate before the final stretch.
Mr Biden successfully channelled sentimental attachments to former President Barack Obama.
About half of North Carolina voters, for example, wanted a president who would restore politics to a pre-Trump era — and Mr Biden, who served as Mr Obama’s vice-president, won the majority of this group.
He did well with moderates and conservatives, voters older than 45 and African Americans.
In many states, he enjoyed an advantage among women and college graduates.
He performed well with voters who attend church at least once a month.