Campaign staff and volunteers were at work at the office Saturday afternoon, the day after police said a gunshot apparently was fired from outside while people were in the office, The Denver Post said. No one was hurt in the incident.
Police said they had a description of a "vehicle of interest" in the shooting but had not provided those details.
A child's rainbow crayon poster decorated a piece of plywood placed over the broken window frame, the newspaper said.
A local spokeswoman for the Obama campaign referred queries to police. State Republican officials had no comment other than to say they were sorry to hear of the incident, the Post said.