Since the bottom of the financial crisis in early 2009, U.S. companies have delivered solid earnings growth, quarter after quarter. That growth has come despite modest sales gains as companies have squeezed costs and become leaner. Profit margins are now near pre-crisis highs. Yet there are plenty of reasons to be skeptical about how well American companies can hold up. The U.S. economy is sluggish and unemployment remains high at 8.2 percent. Also weighing down American companies are Europe's worsening crisis and slower economic growth in the U.S. and China, the world's two largest economies.