Joe Biden and Bernie Sanders are the last White House candidates standing in the Democratic race to challenge Republican Donald Trump in November, after US Representative Tulsi Gabbard of Hawaii on Thursday ended her longshot bid and endorsed Biden.

Democratic US presidential candidates former vice president Joe Biden and Senator Bernie Sanders do an elbow bump in place of a handshake as they greet other before the start of the 11th Democratic candidates debate of the 2020 US presidential campaign, held in CNN's Washington studios without an audience because of the global coronavirus pandemic, in Washington, US March 15, 2020. [Photo/Agencies]

DEMOCRATS

JOE BIDEN

Front-runner Biden, 77, was vice president under former president Barack Obama from 2009-2017. Long a US senator, Biden has had nearly 50 years in US public office and has said this makes him best suited to take over from Trump on Day One.

His campaign, which had been on life support after poor showings in the Iowa and New Hampshire nominating contests, was resurrected by a resounding win in South Carolina. He has since emerged as a consensus champion for the moderate wing of the Democratic Party.

Questions persist about his age and moderate brand of politics, which progressives contend is out of step with the leftward shift of the party.

BERNIE SANDERS

A US senator from Vermont and an independent with an impassioned following, Sanders is making a second White House bid and had emerged as the front-runner before Biden's surge.

He has faced increasing pressure to abandon his campaign since Biden's dominating victories in contests in Florida, Illinois and Arizona, which effectively closed off any viable path to the nomination.

As in his first presidential run in 2016, Sanders, 78, has campaigned as an unapologetic democratic socialist who seeks a political revolution. His signature issue is government-run universal healthcare, and he has again proven to be a fundraising powerhouse.

REPUBLICAN

DONALD TRUMP

President Trump, 73, is the sole remaining candidate seeking the Republican nomination. He remains overwhelmingly popular among Republicans, but has faced criticism from Democrats and some health experts for an initially slow response to the coronavirus crisis.

Trump has made a strong economy a pillar of his campaign, but worries about the crisis have sent financial markets reeling and threatened the jobs of millions of Americans forced to stay home as a safety measure.

Since winning the White House in 2016 in his first run for public office, the former businessmen and reality TV host has become a ubiquitous political force, both through frequent controversies and his prolific Twitter account.

The Democratic-led House of Representatives impeached Trump in December over his request that Ukraine carry out investigations into political rival Biden and his son Hunter. But the Republican-led Senate acquitted him on Feb 5.