COLUMBIA, S.C. (AP) — Democrat Jaime Harrison has picked up backing from several who were among the 2020 presidential field in his challenge to U.S. Sen. Lindsey Graham, and now he’s endorsing his choice for the White House - although admittedly the only Democratic candidate still in the race.

On Tuesday, Harrison - a Democratic Party stalwart who serves as an associate chairman with the Democratic National Committee - officially threw his backing behind Joe Biden, calling the former vice president “a longtime friend to the people of South Carolina” who as president “will continue to be an indispensable ally in making South Carolina a healthier and more vibrant place to live and raise a family.”

Harrison’s official endorsement, in a news release from the Biden campaign, comes a day after Biden and former rival Bernie Sanders appeared in a joint, albeit socially distant, online announcement, in which the Vermont senator encouraged his progressive supporters to rally behind the presumptive Democratic nominee in an urgent bid to defeat President Donald Trump. Sanders dropped out of the race last week.

The announcement came as no surprise from a leading Democrat in South Carolina, where Biden's Feb. 29 primary victory - following a pivotal endorsement from House Majority Whip Jim Clyburn - served as a springboard for his march toward the nomination.

In his pursuit of blocking Graham from a fourth term, Harrison has gotten backing from Biden, as well as other 2020 hopefuls including U.S. Sen. Kamala Harris, who called the former South Carolina Democratic chairman an “advocate for the people," and U.S. Sen. Cory Booker.

He's also supported by Clyburn, who has long been a political mentor for Harrison, his former director of U.S. House floor operations.

Earlier this year, Harrison became the party’s presumptive nominee when economist Gloria Bromell Tinubu suspended her campaign and endorsed him. The 44-year-old has posted record fundraising figures in the race, which he has said would take $10 million to win. Last spring, he received backing from the Democratic Senatorial Campaign Committee, support that brought the promise of help with fundraising and grassroots organizing, both of which would be crucial in trying to flip a Senate seat in the deeply red state.

Since then, Harrison raised $3.5 million in the fourth quarter of last year and had $4.6 million cash on hand to start 2020. Graham, 64, is a popular incumbent seeking a fourth term, supported by Trump in a state where the administration’s favorability remains high and Republicans currently occupy all statewide offices and control both legislative chambers.

Graham has brought in record hauls as well, posting $3.9 million in fundraising at the end of the fourth quarter of 2019, topping his own previous quarterly record and leaving Graham with $10.3 million on hand, according to his campaign.

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Meg Kinnard can be reached at http://twitter.com/MegKinnardAP