Stocks struggled to regain their footing in midday trading Thursday after slipping on worries of a large oil supply glut. Crude's slide is giving airlines a fresh boost. Delta (DAL), American (AAL) and United Continental (UAL) are rallying in the session. But falling oil prices isn't the biggest concern that's keeping JPMorgan's (JPM) private bank portfolio manager up at night. Jack Caffery says 'what really derails are earnings declines.' Positive earnings results are driving shares of T-Mobile (TMUS) higher. The telecom company also added more than 2 million net subscribers in the fourth quarter.