It's Big Dog versus Barack, with Bennet's Butt in the Balance

Okay, this is big.  Bill Clinton has endorsed Andrew Romanoff in the Colorado Senate race.  This strikes me as a potential game changer, although as Allison Sherry reported, the Clinton endorsement of Romanoff is not quite the same as Obama's endorsement of Bennet:

Clinton is not expected to do anything for Romanoff — no fundraisers, no stump speeches — beyond the letter sent out to supporters Tuesday.

I'm sort of curious why Clinton got involved in this race at this point.  Does he earnestly think Romanoff is more electable than Bennet and thought he could make a difference?  Did either Bennet or Obama do something recently to irk Clinton?  Is this a proxy war between the Obama and Clinton teams?

I suppose the main question, though, is what sort of effect this endorsement will have.  This will surely help out Romanoff with his Q2 fundraising efforts.  Beyond that, Clinton is now Romanoff's most visible and most beloved endorser among Democratic primary voters.

The most recent SurveyUSA poll on this race had Bennet leading Romanoff 53-36, with 11% undecided.  That's a huge lead, but this is the only poll we've seen in the past month and a half.  I'd feel a lot more comfortable in the finding if more than one poll were used.  But let's say it's an accurate reading of the Democratic primary electorate.  Can Bill Clinton actually bring the bulk of undecided voters and a chunk of the Bennet voters over Romanoff's way?  

Keep in mind that, unlike general elections, primaries are actually somewhat volatile.  Lacking the party label, primary voters look for some sorts of cues about support and viability.  Endorsements and funding end up being highly influential factors in primary elections.  Today, Bill Clinton substantially eroded Bennet's advantage on both counts.