The nation’s top law-enforcement officer told an African-American sorority Monday that he would lead an effort to change Americans’ beliefs and judgments about race, following George Zimmerman’s Sunday acquittal in the 2012 shooting of Trayvon Martin. Attorney General Eric Holder blamed racial attitudes for the killing. “We are resolved, as you are, to combat violence involving or directed at young people, to prevent future tragedies, and to deal with the underlying attitudes, mistaken beliefs and stereotypes that serve as the basis for these too-common incidents,” Holder told the long-scheduled meeting of the Delta Sigma Theta sorority. Martin was a 17...