U.S. holiday sales growth slowed by more than half this year after gridlock in Washington soured consumers’ moods and Hurricane Sandy disrupted shopping, MasterCard Advisors SpendingPulse said. Retail sales grew by 0.7 percent from Oct. 28 through Dec. 24 — sales grew at a 2 percent pace in the same period last year. Last month, retailers from Macy’s Inc. (NYSE: M) to Target Corp. (NYSE: TGT) posted same-store sales that trailed analysts’ estimates. Two factors affecting lower sales were…