Julián Castro, a former member of Barack Obama's cabinet, has become the latest Democrat to drop out of the 2020 presidential race.
Mr Castro confirmed he was suspending his campaign, a month before the Iowa caucuses mark the beginning of the primary process that will determine which Democrat will face Donald Trump in November.
He said: "I've determined that it simply isn't our time.
"So today it's with a heavy heart and with profound gratitude that I will suspend my campaign for president."
It’s with profound gratitude to all of our supporters that I suspend my campaign for president today.
I’m so proud of everything we’ve accomplished together. I’m going to keep fighting for an America where everyone counts—I hope you’ll join me in that fight. pic.twitter.com/jXQLJa3AdC— Julián Castro (@JulianCastro) January 2, 2020
45-year-old Mr Castro - who was President Obama's housing secretary, as well as a former mayor of San Antonio in Texas - launched his campaign a year ago.
While he received some attention for his performance in debates, he struggled to gain momentum in the polls - with FiveThirtyEight putting his polling average at just 1.1%.
More than a dozen candidates remain in the Democratic race ahead of next month's Iowa caucuses and New Hampshire primary.
The process will see Democrats in individual states vote to choose the party's presidential candidate for the general election in November.
Primaries continue until June, while so-called 'Super Tuesday' on March 3rd - which sees primaries in more than a dozen states - will give an early indication of those with a clear path to the final nomination.
Polls have consistently shown former vice president Joe Biden leading the pack, followed by progressive senators Bernie Sanders and Elizabeth Warren.
Mr Castro joins a number of candidates who've already dropped out of the race - including high-profile figures such as Kamala Harris and Beto O'Rourke.
The monthly televised campaign debates - which so far have seen large groups of candidates take part - now have increasingly stricter qualification criteria, meaning many candidates have struggled to secure the necessary support in the polls and fundraising to make the stage.
