Democratic presidential candidate and former Rep. for Texas Beto O'Rourke speaks at the Iowa Federation Labor Convention on August 21, 2019 in Altoona, Iowa.

Former Texas Senate candidate Beto O'Rourke said Friday that he will drop out of the 2020 presidential race, making him the latest candidate to exit the still-crowded but narrowing Democratic primary contest.

"Our campaign has always been about seeing clearly, speaking honestly, and acting decisively," O'Rourke announced in a series of tweets. "In that spirit: I am announcing that my service to the country will not be as a candidate or as the nominee."

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The announcement also included a link to a lengthy post on Medium, in which O'Rourke vowed to support the eventual Democratic nominee.

"We will work to ensure that the Democratic nominee is successful in defeating Donald Trump in 2020," O'Rourke wrote in the blog post. "I can tell you firsthand from having the chance to know the candidates, we will be well served by any one of them, and I'm going to be proud to support whoever that nominee is."

O'Rourke had told some of his donors earlier this week that he was likely going to drop out, people familiar with the matter told CNBC.

Mark Gallogly, the founder of investment firm Centerbridge Partners and a lead bundler for O'Rourke, told CNBC that "Beto consistently raised important issues with great integrity and energy for all Americans."

O'Rourke, 47, was a U.S. representative from Texas before giving up his seat to run for Senate in 2018 against incumbent Sen. Ted Cruz. His impressive fundraising numbers and large crowds in that race garnered national attention, raising hopes among Democrats that Texas, traditionally a reliably Republican stronghold, could be turned blue.