Julián Castro, the former housing secretary and former mayor of San Antonio, announced on Saturday that he would run for president, one of the most high-profile Latino Democrats ever to seek the party’s nomination. His first campaign stop will be in Puerto Rico, where he will speak on Monday at the Latino Victory Fund’s annual summit and meet with residents still struggling to recover from Hurricane Maria. Later in the week, his campaign said, he will go to New Hampshire. Mr. Castro, in prepared remarks that he was set to deliver in San Antonio on Saturday, said, “When my grandmother...