Over the weekend, Andrew Romanoff turned up at a union-sponsored Labor Day picnic where current U.S. Senator Michael Bennet was also glad-handing -- one reason why a Tuesday blog about his appearance was headlined "Andrew Romanoff Sure Looking Like a Senatorial Candidate." As a result, his decision today to file the paperwork required to explore a bid for Bennet's office -- a precursor to a formal announcement -- was wholly predictable, yet still startling to Dems who figured their biggest Senate election fight next year would involve Republicans rather than one of their own. Which isn't to say Romanoff is ready for a campaign. At this writing, his website, AndrewRomanoff.com, is doing the time warp, taking visitors back to his term as speaker of the Colorado House, and his most recent blog entry concerns a trip to Israel in March. He's got plenty of cyber-work to do before starting a run in earnest, at which point he'll become a target for much of the Democratic establishment that's championed him as an up-and-comer in recent years. With Republican Jane Norton in the exploratory phase, too, the Senate field is on the cusp of expanding in a significant, and politically intriguing, way.