The former San Antonio mayor's numbers, released Monday, lag well behind other contenders in the crowded field of Democrats. He's also short of the 65,000-donor threshold to guarantee a spot in the first debates this summer, though Castro has met the polling criteria to get on the stage.
Castro says he knows he's not a front-runner but believes momentum is building. His campaign says they've raised an additional $570,000 since the start of April.
Castro has made immigration a central part of his early campaign and has vowed to visit all 50 states.
Bernie Sanders leads the money race so far , with the Vermont senator pulling in $18 million.
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