Leave it to the prospect of a primary challenge to influence a Senator. Or leave it to the changing-base of the constituency(essentially the same thing). Whether it be Arlen Specter moving from the prospect of a Republican primary challenge to a Democratic one, or Kirsten Gillibrand expanding her field of play from New York's 20th Congressional District to the entire Empire State, it becomes inevitable for politicians to change their voting pattern. While I remain skeptical of Arlen Specter, as I exclaimed here, I am far less-so on Senator Kirsten Gillibrand.
Indeed, if she keeps up with her with current pace, she'll undoubtedly deserve to be supported by progressives.
This is not to say that there is anything wrong about continued-rumors of primary challenges for the junior Senator from New York. In fact it's often beneficial for any politician to be made to work harder. We have seen this first hand with a certain Kossack named Senator Kirsten Gillibrand who, upon realizing that her voter-base has substantially changed since her appointment, has begun a dialogue that we all certainly hope will continue.
Words may be cheap, but when they are backed up by actions and honesty, they are priceless. Nate Silver, the Kossack formerly known as "poblano", has cited the findings of ProgressivePunch.org to characterize Kirsten Gillibrand as a "lockstep liberal" while in the United States Senate. Per ProgressivePunch's formula, the junior Senator from New York has a score of 98.45%. That makes her the 15th most-progressive member of the Democratic caucus in the U.S. Senate.
While there are still a broad array of issues that Senator Gillibrand has yet to vote or write on(immigration, gun-control, and energy to name a few), the results thus far have been very positive. If she keeps it up she'll certainly deserve support from progressives.