Complex sentence: Glenn resigned from NASA on January 16,1964, and the next day announced plans to run for a U.S. Senate seat from Ohio; however, a bathroom fall which resulted in a concussion caused him to withdraw from the race in March.
Split into simpler sentences: Glenn resigned from NASA on January 16,1964, and the next day announced plans to run for a U.S. Senate seat from Ohio. But injury from a bathtub concussion caused him to withdraw from the race in March.