Not even three months after becoming a U.S. citizen, Kaillie Humphries brought home a gold medal. The monobob gold she won on Monday was her third overall (two-man in 2014 and 2010, when she was representing Canada). Her 1.54-second margin of victory is the largest in an Olympic bobsled race in 42 years. She was given a U.S. flag as she exited her apparatus and, with a grin, she chanted “U-S-A! U-S-A!” “This one feels more emotional than most,” Humphries said. “It just really hits the heartstrings a little bit to know that I had to fight so hard for something that I wanted, and I had the backi…