There are many ways to conceive of this decline. We talk about the 'Obama coalition', the fact that the GOP has only won a majority of the popular vote in a presidential election once since 1988, the shrinking percentage of the electorate made up by white voters.
But there's another way of thinking about this which looks from a slightly different vantage point at the same history. The GOP has won two presidential elections since 1988 - George W. Bush's two terms in 2000 and 2004. But they were both extremely close-run things. Setting side the controversies of the 2000 election, Bush won 286 electoral votes in 2004 and 271 in 2000. In other words, both about as close as you can get in our system.
Meanwhile, here are the electoral votes totals for the Democratic wins in 1992 (370), 1996 (379), 2008 (365) and 2012 (332).
Again, it's not lost on me that this is really only looking at the popular vote majority point from a different angle. But still, it captures a very basic reality: even in the Bush years, when a huge amount of extremely consequential policy decisions were made, the GOP was really just maxing out an already limited electoral coalition.
The obvious and very solid rejoinder to this history is that, "Well, for a dying party they're certainly hanging on pretty well." Since 1994 the GOP has controlled Congress in whole or in part for all but the four years between 2007 and 2011. Republicans currently hold both houses of Congress and it remains quite conceivable that they will still hold both houses of Congress in 2017. Yet, the Democrats actually got more votes for the House in 2012 (over a million more) even as Republicans retained a pretty sizable majority.
In any case, I think this shrinking electoral base, highly driven by demography, is a critical part of the backstory of this election. There's much discussion of the fact that many whites see the prospect of a white majority America slipping away and this election as the 'last chance' to turn back the tide. But another dimension of the story is that as the GOP electoral base has shrunk it has required increasingly apocalyptic arguments and more extravagant promises to activate that base to a sufficient intensity to win elections. But that comes at the cost of slowly degrading their own credibility by painting an escalating cast of horrors and dangers they're never able to solve and in most cases do not even logically address. Most of these promises are simply unrealizable - thus the focus on blocking things rather than pushing an agenda that can sustain popular support. That in turn is I think the root of the now almost total disconnect between GOP elites (the 'establishment') and the bulk of Republicans voters. Trumpers say they've been lied to by their leaders. And in a very real sense they have been.
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