LAS VEGAS—Dick Button has always been the measuring stick for American men figure skaters. And no wonder, with seven straight U.S. titles and two Olympic gold medals. Nathan Chen has leapt into Button territory. Even with an error at the beginning of his free skate, Chen was unbeatable Sunday, winning his fifth straight U.S. Figure Skating Championship. Not since Button won each title from 1946–52 has any American man had such a streak of success. Throw in two world championships and being unbeaten since not medaling at the 2018 Olympics, and Chen already has a resume for the ages. At age 21. “It’s incredible to try to follow in his footsteps,” Chen said of Button. “It means the world. Dick is a true skating icon, and it just feels incredible to be trying to chase something that someone like that has done. I’m nowhere near the level he was at, …