Republicans said it would be a "dereliction of duty" to punt the appointment to the governor.
Tuesday night's gatherings begin the process of deciding which candidates will represent their parties in a variety races in November.
What makes next Tuesday's caucuses so important is the fact that they draw the party faithful who are deeply interested in this race.
Russia is likely to meddle in this year's election. That's what intelligence officials told members of Congress Tuesday morning.
Democrats have used health care to go on the attack, and the issue is coming up in congressional races in Colorado and across the country.
The race for governor is firming up, and along with it the race for campaign funds.
The second annual march is scheduled for Saturday. Organizers are trying to turn it into a movement focused on state politics.
The move had been anticipated since Republican Attorney General Cynthia Coffman announced she was entering the governor's race last week.
Democrats say the large swing in Virginia shows it's possible for them to flip other chambers next year, including the Colorado Senate.