Doubt on the Left about Udall's Electability

When a blog named "An Enduring Democrat Majority" titles a major piece CO-Sen: Is Udall the Favorite in Open Seat Contest? you know that there are many on the self described Progressive Left who fear that Mark Udall is too far to the left for Colorado. They say as much:

Udall has considered statewide runs previously, but had opted out fearing his "Boulder Liberal" label made him unattractive to the Colorado electorate. The state's recent shift toward the Democratic Party and Udall's efforts to move towards the middle appear to have changed this analysis...

Could anything deter Dems from picking up this seat, widely regarded as our top 2008 pick up opportunity? There are concerns about a 'drag' or 'reverse coat-tails' affect in Colorado if the national party's presidential nominee is unpopular in the region. News reports quoted the Udall campaign as having an eye on the presidential race - concerned about the top of the ticket potentially hurting their chances. More on the electability issue as the campaign wears on.

Not that we are keeping score, but that is the fourth liberal or left source to express that fear or observation.