Summer is over. And Donald Trump is -- still -- at the top of the 2016 Republican primary field.

That makes lots and lots of Republicans with an eye on winning the White House in 2016 (or even 2020) very, very nervous. That unease -- and its origins -- are explained brilliantly in this paragraph, taken from a broader piece entitled "The GOP is Killing Itself," by former Bush administration official Pete Wehner:

The message being sent to voters is this: The Republican Party is led by people who are profoundly uncomfortable with the changing (and inevitable) demographic nature of our nation. The GOP is longing to return to the past and is fearful of the future. It is a party that is characterized by resentments and grievances, by distress and dismay, by the belief that America is irredeemably corrupt and past the point of no return. “The American dream is dead,” in the emphatic words of Mr. Trump.

Wehner, whose honesty and insight about his party and its prospects I've praised before in this space, nails a sentiment I've heard expressed by countless Republicans in the Summer of Trump. The concern is that a candidate like Trump is running a campaign based on the 1980 electorate, not the 2016 one.

Sure, appealing to white voters with a message that things aren't as good as they used to be -- the boiled-down appeal that Trump represents -- might work in a Republican primary. But, there is NO mystery or debate that the changing demographic face of the country makes an appeal to the "old ways" an almost-certain electoral loser.

Consider that the white vote as a percentage of the overall electorate has dropped in every election since 1992 -- and dipped to 72 percent in 2012.

And, even as the white vote has become increasingly less influential in presidential general elections, Republicans have grown increasingly unable to compete for the Hispanic vote, which is growing by leaps and bounds. In 2004, George W. Bush won (a somewhat-disputed) 44 percent of the Hispanic vote. That dropped to 31 percent for John McCain in 2008. Mitt Romney won just 27 percent of the Hispanic vote in 2012.

This chart tells the story of just how white Romney's support was in that election.

This, from the brilliant Dan Balz, sums up what all those numbers mean for Republicans in 2016:

If the 2016 nominee gets no better than Romney’s 17 percent of the nonwhite vote, he or she would need 65 percent of the white vote to win, a level achieved in modern times only by Ronald Reagan in his 1984 landslide. Bush’s 2004 winning formula — 26 percent of the nonwhite vote and 58 percent of the white vote — would be a losing formula in 2016, given population changes.

Simply put: There is no long-term coalition for a party that touts "the way things were" and pushes a policy of rounding up and deporting the millions of undocumented immigrants in the United States. None.

Strategists like Wehner know this. The problem is that people like Trump not only have a much bigger megaphone but also a vested interest in pushing policies that appeal to a niche -- albeit a somewhat large niche -- of the Republican base.

Trump is playing the GOP primary game better than anyone else in this race. But he is putting his party in a losing position -- or taking them to the verge of it -- when it comes to a general election in which we know a message like his will (or already has) turned off large numbers of people that the GOP desperately needs to build a national coalition.

The problem with all of this, of course, is that Trump could care less about what Wehner thinks. In fact, Trump would likely tout Wehner's argument as evidence that the Washington party establishment is a failed, clueless lot.

The only person who can control or manage Trump is Trump. And he seems to have little of the party's long-term interests in mind at the moment. Commence panic.

What Donald Trump is doing on the campaign trail

U.S. Republican presidential nominee Donald Trump speaks at a campaign event at Trump Doral golf course in Miami, Florida, U.S. July 27, 2016. REUTERS/Carlo Allegri (Carlo Allegri/Reuters)