There are some people who graduated from Korean medical schools in recent years and practice medicine here at the US. Yes, you will have a lot of competition from other foreign medical graduates. And it’s harder to get into a residency spot compared to 10 years ago. (There are more US graduates but residency spot haven’t increased.) And you cannot get into a competitive field such as surgery or dermatology. You may have chance for unpopular fields such as psychology, neurology, anesthesiology or internal medicine. But for even those fields, you will need to have excellent test scores and good interviews. It’s doable but it’s not going be easy. If you’re not a superstar student, working at an US research lab can a stepping stone to have a foot in the door.