This is what you get when Hillary refuses to campaign in a state - or told by advicers not to. Not a smart decision exactly. She could have energized latinos like crazy there.
Colorado is not a Hillary-friendly state. When PPP polled this race in July, when it still leaned toward Udall, it found Hillary leading Ted Cruz by just 1 percentage point. Hillary would not have helped Udall, and might even have set him back.
Source: http://www.publicpolicypolling.com/pdf/2014/COMiscResults.pdf
I know it's not, however latinos there are, and that is all that matters as long as Udall was seen as a clear underdog.
Besides I think that Hillary's numbers in Colorado is mostly a mirror of the current Democratic politician fatigue that the state's residents are experiencing (Obama + Hickenlooper + the entire legislature, as well as Udall obviously). Only one party is getting all the blame in Colorado, unlike what's the case in most other states, and certainly in most other battleground states. Compare that to Kansas, North Carolina and Georgia where Republicans are getting most of the blame.
