LAS VEGAS — A prominent antipoverty organization that drew criticism from Republicans during last year’s presidential race was charged by Nevada officials Monday with engaging in voter registration fraud. Two former leaders of the group’s Nevada branch were also charged in connection with the submission of thousands of bogus voter registration forms. The organization, the Association of Community Organizations for Reform Now, or Acorn, is accused of paying canvassers only if they registered at least 20 voters per shift and providing bonuses of $5 for registering more than 21. Under Nevada law, it is illegal to attach incentives to such...