There has been very little head-to-head polling of Collins vs. Gideon (and the few recent ones we've had show a close race), so I would hesitate to call this Lean D yet. It should also be noted that in the past much of Collins' disapproval in past polling came from conservative Republicans who would ultimately vote for her.
With that said, the trajectory of the race is clearly not favorable to Collins and it should be much more competitive than some here were initially expecting.
Well put. I would note that many have Margeret Chase Smith as a comparison to Collins; but they forget that even she, legendary as she was, was toppled by a liberal Democrat in 1972. So they really didn't think the comparison fully through.