Ask The Blogger: A Phase Change For Republicans?

A reader asks:

The notion occurred to me and your scientific literacy compelled me to share. The Republican Party according to Chris Cillizza is now 21% of the population. We don't have a lot of precedent for such low party ID numbers, but does a decline in party ID always have a merely proportionate effect on its influence? Or at some point does a small marginal change have a dramatic effect, akin to a phase change in physics? If there is such a point, did we just pass it?

I love this question and this metaphor. But I don't think it is an accurate way to describe the world... in part because there are plenty of conservatives who will vote Republican but who won't tell pollsters they're Republican because of the brand identity.  I think the phase change metaphor applies to one set of numbers:  the percentage of the time the leaders of the Senate can get 60 votes. If there are 60 Democratic senators, everything changes instantly. 59 senators... not so much. The real phrase change in American politics could occur in 2010... That said, the Republican shrinkage phenom is real, and it's one reason why Americans are giving Obama the benefit of the doubt, policy-wise.