Washington (CNN) - Colorado Gov. Bill Ritter has decided not to run for re-election this November, a Democratic Party source tells CNN.
Ritter, a Democrat who comfortably won a first term in 2006, was facing a tough re-election battle against former Republican Rep. Scott McInnis.
Both the Cook Political Report and the Rothenberg Political Report, two well respected non-partisan analysts, considered the race a toss up. There are 37 governorships are up for grabs in 2010, with Democrats defending 19 seats and the GOP 18 seats.
Colorado will become the 11th open seat the Democrats have to defend. The Republicans are also defending 11 open seats.