A gunshot was fired Friday afternoon at the Obama campaign office in Denver, Colorado, a police spokeswoman said.
While no one was injured during the incident, people were inside the building at the time, police spokeswoman Raquel Lopez told The Denver Post.
Detectives are pursuing a "possible vehicle of interest," she said, but did not provide further details.
A photograph was posted on Twitter showing one of the office's large front windows broken out. By early evening, the window debris had been removed and a glass company was putting up plywood, the newspaper reported.
An Obama campaign spokeswoman declined to comment on the incident.