There is one image from these last few days in Colorado that is going to stick with me, and it is perhaps an unlikely one.  Gabe Cohen , a 33-year-old white guy in a Patagonia jacket, knocks on the screen door of a ranch house belonging to middle-aged black voter. “Hi there,” he says. “I’m with the president’s campaign.” The voter smiles. That’s it. What struck me right then was the power in the word “president,” and the power of what it meant, in that racially mixed neighborhood on the outskirts of Denver, for that word to mean not “them,” but “us.” And that, for a fleeting moment at least, the “us” here was a kind of community encompassing both a white Jewish kid and an older black man. It is an aspirational “us” that, as we saw last night, drove Latinos, and young people, and women, and African-Americans to the…