No, you are wrong there - what Krugman says comes right out of the Census Bureau annual report: median family income increased over 5% in 2015 over 2014.  You can read that big story yourself in the New York Times or even, I believe, in the Register-Guard.  How you can read the words and use them to come to the opposite conclusion baffles me.

Krugman is talking about economic policy, which is (unfortunately) intensely partisan.  In general, the Democratic fiscal policies are based on Keynseian stimulus, while Republican policy since Reagan has been "supply side" tax breaks, also called "trickle-down" or "voodoo" economics, which have been shown time and again to reduce revenue, increase deficits, do nothing for working people, and enrich the already rich.  That is a huge difference, and for 99% of Americans, Democratic economic policy is the only rational choice.  That is why Republicans rely on "populist" social issues such as race baiting, religious conservatism, xenophobia, war.