Secretary of State Scott Gessler told The Denver Post that "violently graphical" threats were made against his wife and daughter.
He said he returned home on Aug. 31, a day earlier than planned, at the advice of the Colorado Bureau of Investigation.
A Democrat running for the Legislature has blasted Gessler for using state money for travel to the political convention.
The fee for returning to Colorado early was $422.
Gessler told the Post that his wife and daughter were briefly moved out of the family home because of the security threat.
(Copyright 2012 by The Associated Press. All Rights Reserved.)