Castro, a fast-rising star within the party who gained prominence with his keynote speech at the 2012 Democratic National Convention, will headline a fundraiser hosted by Sen. Tom HarkinThomas (Tom) Richard HarkinDem Senator open to bid from the left in 2020 Senate GOP rejects Trump’s call to go big on gun legislation Trump should require federal contractors to follow the law MORE (D-Iowa), according to the Des Moines Register.

Castro's well-received speech helped give him a national platform, and he's been a vocal supporter of immigration reform. Though Castro has ruled out a run for the presidency in 2016, his office touted a poll showing him as a popular choice to be vice president earlier this summer.