Senator Elizabeth Warren will end her presidential campaign after a poor showing on Super Tuesday.
A favourite of the liberal left, the Massachusetts senator had been a frontrunner in the Democratic field.
However, Ms Warren, 70, failed to convert early excitement into votes.
The Democratic contest to take on President Donald Trump is now seen as a two-horse race between former Vice-President Joe Biden, 77, and Vermont Senator Bernie Sanders, 78.
Ms Warren’s endorsement will now be highly sought after by both candidates.
Her departure will clear the path for Mr Sanders in particular, now the sole progressive candidate left in the race.
With Ms Warren’s departure, a Democratic race that began with a record high of female candidates is now effectively left to two male front-runners.
The erudite Ms Warren vaulted into the political arena more than a decade ago as she pushed for tougher regulation of the financial sector after the 2008 economic collapse.
She championed the creation of the Consumer Financial Protection Bureau – a government agency that would serve as a Wall Street watchdog.
In 2010, she helped the Obama White House set it up.
Two years later, the former Harvard law professor rode that momentum to a seat in the US Senate for Massachusetts.