"I think that competition is good in our party", the senator from Minnesota said, telling Harlow that former President Barack Obama has been telling 2020 candidates that he believes the more the merrier in the nomination fight. "I think it's important to have people that are running from different parts of the country".
Fellow Texan Julian Castro distributed a list of Texas Democrats who had already gotten behind the former federal housing chief's campaign.
O'Rourke, a former punk musician who sometimes went skateboarding to blow off steam on the Texas campaign trail, may quickly achieve rockstar status if he runs.
'You can probably tell that I want to run, ' he says.
He also held a rally in El Paso on the same night in February that Republican President Donald Trump staged one there.
Beyond a previously announced event in Waterloo, Iowa, on Saturday, O'Rourke is expected to visit other towns in eastern Iowa, traditionally a Democratic stronghold.More news: UEFA Champions League Quarter-Final Draw Revealed
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O'Rourke, a 46-year-old former three-term USA representative from West Texas, made the announcement online.
Mr O'Rourke was little-known outside his hometown of El Paso until he challenged Republican Senator Ted Cruz a year ago.
Like progressives such as Sanders, O'Rourke premised much of his appeal in the Senate race on his refusal to accept money from political action committees and instead raised $80 million from small-dollar donors - a national record for a Senate bid. But O'Rourke's momentum seemed to be revived in a big way last month amid the debate over building a wall along the Mexican border - right along his hometown of El Paso.
O'Rourke, whose given name is Robert Francis, as a child acquired his nickname "Beto", a common shortening of "Roberto" for Spanish speakers.