Voters in more than 100 Colorado cities and towns will cast ballots in local elections April 1 and April 8.
Hill becomes the 3rd republican to drop out of the Senate race after Gardner announces run
Precinct caucuses kick-off election season in a year where Colorado Republicans hope to unseat Governor John Hickenlooper and Democratic U.S. Senator Mark Udall.
Colorado's Senate seat could be the key to which party controls Congress next year.
In order to hold the seat, Zenzinger will have to survive an election next November where voters in the highly-competitive district are almost evenly divided between Democrats, Republicans and unaffiliated.