"It’s true about almost any major indicator: gross domestic product, employment, incomes, productivity, even stock prices. It’s true if you examine only the precise period when a president is in office, or instead assume that a president’s policies affect the economy only after a lag and don’t start his economic clock until months after he takes office. The gap “holds almost regardless of how you define success,” two economics professors at Princeton write. They describe it as “startlingly large.”Since 1933, the economy has grown at an annual average rate of 4.6 percent under Democratic presidents and 2.4 percent under Republicans. In more concrete terms: The average income of Americans would be more than double its current level if the economy had somehow grown at the Democratic rate for all of the past nine decades."