Washington Mutual’s (WM) stock fell about 12.5% in mid-morning trading on Wednesday to $2.03 a share amid fears that the battered bank is facing more trouble ahead as adjustable-rate mortgages reset. The stock plunge followed Standard & Poor’s Ratings Services’ decision to lower its outlook to “negative” from “stable” after Washington Mutual booted CEO Kerry Killinger. The bank’s stock has lost about 95% of its value in the last 52 weeks. “The outlook revision reflects the increasingly challenging housing and mortgage markets and their impact on WaMu’s core mortgage franchise ” S&P Credit Analyst Victoria Wagner said in a ...