Twitter CEO Dick Costolo is taking personal responsibility for his platform's chronic problems with harassment and abuse, telling employees that he is embarrassed for the company's failures and would soon be taking stronger action to eliminate trolls. He said problems with trolls are driving away the company's users...In November, Twitter partnered with an advocacy group called WAM! to investigate harassment against women. But every day, Twitter users still face threats of physical violence, sexual abuse, and stalking — all forms of harassment that disproportionately affect women