WASHINGTON - Americans vote Tuesday in primaries that play a major role in who will challenge Donald Trump for the presidency, a day after key endorsements dramatically boosted Joe Biden's hopes against surging leftist Bernie Sanders.
The backing of Biden by three of his ex-rivals marked an unprecedented turn in a fractured, often bitter campaign.
The Democratic establishment is desperate to unite around a moderate candidate who can triumph over frontrunner Sanders, a self-described democratic socialist, and face President Trump in November.
Voting begins as early as 6:00 am (1100 GMT) in some areas.
As the five remaining Democratic candidates made their final pitch to voters in 14 states, Biden was capitalizing on momentum he seized at the weekend with a blowout victory in South Carolina.
The 77-year-old former vice president is consolidating support among moderates eager to blunt the advance of Sanders, who could take a potentially insurmountable lead in the all-important delegate count after Super Tuesday.
Biden has been riding high with key endorsements that built into a political crescendo on Monday.
He took the stage at a rally in Dallas, Texas joined by Minnesota Senator Amy Klobuchar, who told the crowd she was ending her campaign and endorsing Biden for president.
Biden later introduced Beto O'Rourke, who made a big splash early in the Democratic race but then fizzled out. O'Rourke remains popular in Texas, the state with the largest delegate haul on Tuesday after California.
"We need somebody who can beat Donald Trump (and) in Joe Biden we have that man," O'Rourke said, peppering his short speech with Spanish.
ion needs: fair pay, affordable housing, equal rights," she said. (AFP)