HOUSTON (Reuters) -- Former Vice President Joe Biden's Democratic presidential bid picked up steam on Monday as he was set to pick up the endorsements of two former 2020 rivals -- Amy Klobuchar and Pete Buttigieg -- on the eve of the crucial Super Tuesday primary elections
Klobuchar, a U.S. senator from Minnesota, will become the third 2020 candidate in as many days to drop out of the race when she announces the suspension of her campaign in Dallas, where she will also publicly back Biden, a Klobuchar aide said.
Former South Bend, Indiana, Mayor Buttigieg, who ended his White House bid on Sunday, also plans to endorse Biden in Dallas, a top adviser said.
Biden is fresh off a resounding victory in Saturday's South Carolina primary and is aiming for a strong showing on Super Tuesday against U.S. Senator Bernie Sanders, the national front-runner and a democratic socialist from Vermont.
But Biden also faces a challenge from billionaire former New York Mayor Michael Bloomberg among voters hoping the party will nominate a moderate.
The Super Tuesday contests offer the biggest one-day haul of the 1,991 delegates needed to win the party's nomination at its national convention in July, with about 1,357 delegates, or nearly one-third of the total number, up for grabs.
Fourteen states -- California, Texas, Virginia, Massachusetts, Tennessee, Alabama, Arkansas, Oklahoma, Minnesota, Vermont, Colorado, Utah, North Carolina and Maine -- as well as American Samoa and Democrats living abroad cast ballots on Tuesday. (The primary for expatriate Americans is scheduled to run through March 10.)
Bloomberg, a late entrant to the race, will make his ballot-box debut. He is betting the $500 million of his own money he has poured into his campaign will allow him to make up for not competing in Iowa, New Hampshire, Nevada or South Carolina.
Five candidates -- Biden, Bloomberg, Sanders, U.S. Senator Elizabeth Warren of Massachusetts and U.S. Representative Tulsi Gabbard of Hawaii -- remain in the running for the nomination to take on Republican President Donald Trump in November's election, down from more than 20 earlier in the campaign.
Bloomberg and Biden have emerged as the main contenders for the votes of moderate Democrats while Sanders is the progressive front-runner nationally, eclipsing Warren.
Biden's high-stakes triumph in South Carolina, where his campaign had said his popularity with black voters would propel him to victory after early disappointing finishes in Iowa and New Hampshire, helped winnow the field.
In addition to Klobuchar and Buttigieg, billionaire environmental activist Tom Steyer also gave up his campaign on Saturday night after a third-place finish in the Southern state in which he had invested most heavily.
Already, one of Buttigieg's top fundraisers, who spoke on condition of anonymity, said some of the former mayor's supporters planned to donate to Biden's campaign.
However, Sanders' momentum might not be easily slowed. On Monday, his campaign downplayed the efforts by moderates to present a united front.
"The establishment is nervous, not because we can't beat Trump, but because we will," said Sanders' campaign manager, Faiz Shakir. "And when we do, the Democratic Party will again be a party of the working class."
Indeed, it was not immediately clear who would immediately benefit from departures by Buttigieg and Klobuchar. A Morning Consult poll taken Feb. 23-27, for example, before Buttigieg exited the race, showed that 21% of his supporters named Sanders as their second choice, 19% picked Biden, another 19% chose Warren and 17% favored Bloomberg.
Biden still lags his rivals in spending and organization in Super Tuesday states and beyond, but his campaign said on Sunday it had raised more than $10 million over the preceding two days.
Biden's campaign has also touted endorsements from more than 70 elected officials and community leaders since South Carolina's primary that could lead to a boost in attention for Biden ahead of Super Tuesday.
In Virginia, U.S. Senator Tim Kaine has endorsed him, along with state House Majority Leader Charniele Herring. In Colorado, Denver Mayor Michael Hancock has backed Biden. In California, U.S. Representative Gil Cisneros is supporting the former vice president.