I was afraid to read it, because I don't want my hopes raised and then crushed. The current polls, for what they are worth, don't show a GOP cruising for a bruising. Greenberg's main claim is that John B. Judis and Ruy Teixeira were right way back in 2004 when they predicted an Emerging Democratic Majority.
I think the change based on 11 years of information is a greater stress on the beliefs of currently young Americans about religion and gays (also marijuana but Greenberg didn't mention that green stuff). They key paragraph is
... a new majority coalition of racial minorities, single women, millennials and seculars. Together, these groups formed 51 percent of the electorate in 2012, but our analysis of census survey data and exit poll projections indicates that they will comprise fully 63 percent in 2016. With these growing groups each supporting Hillary Clinton by more than 2 to 1 in today’s polls, it is fair to say that the United States has reached an electoral tipping point.I think the growth of seculars is a bit of a surprise (they are people don't identify with any organized religion a majority of whom are neither atheist nor agnostic). But I think the key question is whether millennials will keep their current views which are similar to mine and very different from those of a majority of US citizens of my age. Another question is whether US Hispanic whites will continue to be a racial minority (as US Irish, Italians and Poles once were) or whether they will come to consider themselves part of roughly the same group as WASPs.
The point is not new (it probably wasn't new in 2004 either). To me the really interesting thing about the article is the name of the author. Greenberg has made a career studying the difficulties Democrats have have regaining the support of Reagan Democrats/blue collar ethnics/working class whites recently here. In this article, he argues that that group, which he studied and studied is no longer politically crucial. It is almost as if Mudcat Saunders wrote that he was convinced by Thomas Schaller's thesis in "Whistling Past Dixie" (I see it was published in January 2008 so Schaller sure didn't have to wait as long as Judis and Teixeira for confirmation).
I am not really surprised that Greenberg goes where the data lead him -- I have often been impressed by his research. But I am pleased. I think his narrow economic interests would have been well served by acting as the debater contra Judis and Teixeira. I don't think there is any advantage for public intellectuals gained by noting that the world has changed and that the things they said about the past are not true of the present. I think it helps to be predictable (I'm sure it helps them get on TV as bookers want to know what guests will say). Now Greenberg is in a different league than Sanders or the talking heads. Top Democrats will listen to him even after he has changed his emphasis. He wants them to win elections so he doesn't just want to take their campaign money, he wants to give them good advice. Still I am pleased (and displeased that I am surprised enough to be pleased).
Greenberg suggests that the new Republican and Conservative extremism is a reaction to the knowledge that people of my age race and gender won't control our shared country for long. This is the natural if uncharitable guess of what tea partiers really mean when they say they want to take our country back. Here it is important that, following party affiliation, voting intention, and issue polling, he considers key groups to be single women vs married women and men whether married or single (lots of tea partiers are women but few are single women). I know very few US conservatives and very few Republicans, but I am sure he is right. They talk and write about tipping points and some sort of doom. I am sure it is demographic doom.
I am out of touch (I am typing this in Rome). I am surprised that 15% of new marriages include spouses of different races (always counting Hispanic and Anglo white as different). I am shocked and appalled that only 68% of US adults think that "Sex between and unmarried man and woman" is "morally acceptable". I mean what the fuck do they expect single adults to do ? I guess it is impressive that this is only 5% more than the 63% who think gay sex is morally acceptable (still way too low but much higher than it was). I guess the dramatic news is that attitudes towards gay sex and premarital heterosex are similar, but I think it bears repeating: what the fuck ?