Senator Clinton announced yesterday that Raul Yzaguirre, a prominent Hispanic activist and former president of the National Council of La Raza, would co-chair her presidential campaign and lead its outreach to Hispanic voters. “Hillary Clinton has spent more than three decades advocating on behalf of those who are invisible in America,” Mr. Yzaguirre said in a statement. “Senator Clinton has the ability to bring people together to get results and move this country forward.”