No one was injured, The Denver Post reported. Raquel Lopez, a police spokeswoman, said there were people in the office at the time.
"It looks like it was one shot that was fired into the structure," she said.
No one had been arrested late Friday. Lopez said police had a description of a car that might have been used by the shooter.
A campaign spokeswoman declined to comment on the shooting.
Costly malfunction causes beer flood at Boston-area brewery
Video of Victoria’s Secret models trying to 'twerk' hits Instagram