The word of the year 2016 has to be "nationalism". All over the developed world, electorates seem discontented with elites who were too quick to embrace immigration and trade, too unwilling to value native culture, native workers, native interests over those of foreign lands. Donald Trump's campaign has some unique American twists, but when you pull back the camera, he looks like part of a pattern of resurgent nationalism, nativism, a desire to hear a politician stand foursquare for "Us" against "Them".
Mr Trump has played on that desire very well, of course. At least, until now. Then yesterday he gave a press conference where, among other things, he invited Russia to find and release missing e-mails from Hillary Clinton's private server.
The possibility that Russia has been trying to influence this election has already been raised by reporters and Democrats. Mr Trump seems to have a lot of Russian money in his projects, and his advisers have close ties to Vladimir Putin's regime. He's also considerably friendlier toward Mr Putin than Republican candidates are wont to be. And the feeling seems to be mutual; Russian media backs Mr Trump, and there are credible allegations that the recent leaks of Democratic National Committee e-mails, which started the Democratic convention on a chaotic note, were the product of a hack by Russian intelligence services.
This argument is the sort that generally stays within the wonk community. It's a complicated "follow the money" story. But most readers (voters) are not going to sit still through your 15,000-word tour of banking statements and legal filings.
Mr Trump's pronouncement was the sort of gaffe that every voter can understand and resent. It's a statement that seems precision-calibrated to alienate exactly the nationalists whose votes he's seeking.
"Nationalism" is a bit of a dirty word because people have done some very bad things in its name. However, they also did some good things, like building modern nations. The sense of the nation as an important source of identity is rather modern, and while it has been the cause of wars, that identity was also absolutely necessary to get all those folks to do anything together. Tribalism, for all its flaws, is one of the main vehicles that human beings have for collective cooperation.
Inviting a foreign power to start attacking Ms Clinton seems like a first-class way to engage voter nationalism. No matter how much one faction of the American tribe may hate Ms Clinton, she's still an American, and this is still a US election. If we have to choose between having our president selected by other Americans we dislike or swayed by the government of another country, I suspect that most of us would prefer to stick with our fellow Americans.
I was sceptical that the rumours that Mr Putin was trying to help Mr Trump get elected would actually matter. On the other hand, when Mr Trump starts soliciting that help, that certainly raises some alarms.
In Mr Trump's thumping rhetoric, voters found the nationalist strain they've been looking for. But his statement yesterday makes it sound as if Mr Trump doesn't really feel any of that sentiment. He's perfectly happy for his country to be manipulated by foreigners, as long as this happens to advance the interests of one Donald J Trump. ©2016 Bloomberg View
Megan McArdle is a Bloomberg View columnist who writes on economics, business and public policy.