NEW YORK TIMES: Over the past five years, as demands for reform have mounted in the aftermath of police violence in cities like Ferguson, Mo., Baltimore and now Minneapolis, police unions have emerged as one of the most significant roadblocks to change. The greater the political pressure for reform, the more defiant the unions often are in resisting it — with few city officials, including liberal leaders, able to overcome their opposition.They aggressively protect the rights of members accused of misconduct, often in arbitration hearings that they have battled to keep behind closed doors. And they have also been remarkably effective at fending off broader change, using their political clout and influence to derail efforts to increase accountability. MORE