NEW YORK — A key federal program designed to cushion health insurers’ risks in the Obamacare exchanges has a massive shortfall, which could throw some insurers into financial turmoil. Insurers requested $2.87 billion in so-called “risk corridors” payments for 2014, but will only receive $362 million, or 12.6%, said the Centers for Medicare & Medicaid Services, which oversees Obamacare. The risk corridors program’s goal is to help insurers transition into the individual exchanges, which opened in 2014. Insurers had a tough time setting premiums since they didn’t know how sick their new customers would be. Under the three-year program, insurers...