Beto O’Rourke is running for the Democratic nomination for president, according to two Democrats familiar with his plans.

O’Rourke was prepared to make a formal announcement on Thursday and planned to head to Iowa, the site of the first 2020 caucus, one of the Democrats said, but word began to get out on Wednesday night. The two Democrats spoke on the condition of anonymity to discuss O’Rourke’s campaign.

The former Texas congressman narrowly lost a Senate contest to Republican incumbent Ted Cruz last fall but managed to build a nationwide following with his unconventional and optimistic style combined with a populist message that brought in almost $80 million in mostly small donations.

Speculation and doubts about O’Rourke’s intentions were fueled by his musings on blog posts as he traveled about the country after leaving Congress at the beginning of January. “Have been stuck lately. In and out of a funk,” he wrote on Jan. 16.

Early polls of potential Democratic nominees put O’Rourke, 46, in the top tier of candidates. But his challenge will be to show the party’s voters where he fits between the unabashed progressive stances of Senators Bernie Sanders and Elizabeth Warren and centrists such as Senator Amy Klobuchar.

Senators Kamala Harris and Cory Booker are attempting to straddle party factions with their campaigns.

Last month, O’Rourke and the man he hopes to unseat, President Donald Trump, held dueling rallies in Texas, with each using the president’s proposed wall on the U.S.-Mexico border as an early proxy for the 2020 election.

Vanity Fair published a long article about O’Rourke on Wednesday evening, with photographs by Annie Leibovitz. In it, he said of a presidential run: “I want to be in it. Man, I’m just born to be in it.”