The struggling retailer bought some breathing room through moves to raise more than $1.5 billion in recent weeks, but investors are growing increasingly doubtful that Sears will ever get back on track. The cost of insuring the retailer’s bonds hit new highs and its stock price continues to tumble falling 5% Monday to close at $6.52, an all-time low, signaling fresh concerns about the retailer’s future Sparking the latest bout of investor anxiety were downgrades of Sears’s debt last month by Fitch Ratings and Moody’s Investors Service that were prompted by the retailer’s dismal holiday sales and continued losses.