Democrat Kamala Harris announced on Tuesday that she was ending her 2020 White House bid after campaign turmoil and disappointing fund-raising in a crowded field.
"I've taken stock and looked at this from every angle, and over the past few days have come to one of the hardest decisions of my life," the senator from California told supporters by email.
"My campaign for president simply doesn't have the financial resources we need to continue."
Ms Harris, 55, was the only African-American woman seeking the Democratic presidential nomination.
She rocketed towards the top of the field with a promising campaign launch in January, but her prospects slid in recent months as she struggled to define her position on domestic issues including health care.
Ms Harris is one of the biggest names to drop out of the race, along with former congressman Beto O'Rourke of Texas and New York Mayor Bill de Blasio.
After stagnating in fifth place in the polls, with about 3.4 per cent support, she was bumped to sixth out of 16 candidates after billionaire former New York mayor Mike Bloomberg recently decided to run.
"I'm not a billionaire. I can't fund my own campaign," she wrote to supporters. "As the campaign has gone on, it's become harder and harder to raise the money we need to compete."
It was shot at rivals including Mr Bloomberg and billionaire activist Tom Steyer, and an indication of the amount of money a candidate needs for a viable campaign in today's political environment.
Ms Harris has been one the fiercest critics of Donald Trump among the 2020 candidates, directly attacking the embattled president and repeatedly calling for his impeachment.
She also challenged Democratic frontrunner Joe Biden head-on in the party's first presidential debate, which proved to be a strategic mistake as her support slid while his largely held.
Ms Harris quickly received accolades from other candidates on Twitter after her premature exit from the race.
"Her campaign broke barriers and did it with joy. Love you, sister," said fellow senator Cory Booker, the other black candidate in the 2020 race.
Ms Harris was the third candidate to drop out in recent days, along with low-polling Montana Governor Steve Bullock and former congressman Joe Sestak.
