One day after the nation celebrated a muted Thanksgiving, malls and retailers imposing strict COVID-19 rules saw fewer Americans in stores for the traditional Black Friday start of the holiday shopping season. But it could drive legal challenges against similar rules placed on houses of worship in other U.S. states. Some politicians and health experts have said that Americans traveling for the Thanksgiving holiday could spread the contagion even faster and push the already strained healthcare system to the brink. Many Americans heeded the advice to stay home for Thanksgiving on Thursday. Nearly 6 million Americans traveled by air from Friday to Wednesday, it said, a number that is however less than half that of the same period last year.