WHEN historians come to write about the 2016 Presidential election, one moment may stand as emblematic of the Republican primary campaign. It occurred on May 2, when Ted Cruz confronted a Trump protester in Indiana. Mr Cruz, a debating champion who has been an advocate before the Supreme Court, made point after point about the gap between Mr Trump's public image and his record and private rhetoric. He might as well have been speaking Swahili. The protester is openly mocking in his attitude, countering detailed points with cries of "Lying Ted". Mr Cruz, who has spent a career pandering to the conservative fringe on issues such as gun rights or Obamacare while denouncing the establishment, found that he was dismissed as yet another member of the elite; as a populist, he had been literally Trumped. Sloganeering has always been part of elections, of course; remember "Yes, we can" and "Hope and change". But Barack Obama (and his opponents, John McCain and Mitt Romney) also offered detailed policy proposals in their campaigns that they had to defend in debates. It is far from clear what Mr Trump believes in; where he has concrete policies, such as on the economy, they are completely implausible. His supporters aren't interested in the details; it is the broad sweep (anti-immigration, isolationist) that they like along with the impression of decisiveness that he creates. In that sense, his appeal resembles that of a Latin American caudillo, or strongman.

When the ancient Greeks contemplated the idea of full democracy, they worried that emotional appeal, rather than reason, would sway the crowd. Plato wrote that

Popular acclaim will attend on the man who tells the people what they truly want to hear rather than what truly benefits them

That phrase might have been invented for Trump. Plato also worried that

an excessive desire for liberty at the expense of everything else is what undermines democracy and leads to the demand for tyranny. A democratic society in its thirst for liberty may fall under the influence of bad leaders

Of course, Plato was an unabashed elitist who believed that societies should be ruled by specially-chosen "guardians". But the idea that there needed to be a filter between the popular vote and political power survived into modern times; it can be clearly seen in the writings of the founding fathers. The Senate was unelected until the 20th century and expected to act as a check on the democratically-elected House; the electoral college was also supposed to let the great and the good exercise influence over the choice of President. These filters dropped away but until recently, the party elites still exercised some control over the primary system through endorsement of candidates and fund-raising. In Britain, party leaders always needed the support of their elected MPs. The success of Trump, and Jeremy Corbyn in last year's Labour leadership elections, has swept away those lingering vestiges of elite control.

Jolly good, many may say. Not only was the old system undemocratic but the elites completely cocked things up, opting for a disastrous war in Iraq and allowing the financial sector to crash the economy in 2008. On the other hand, one shudders to think what might have happened to the US economy had Congress listened to voters and refused to bail out the banks under George W. Bush or push through a fiscal stimulus under Obama in 2009.

It is also worth noting that both the US primary system, and the system for electing Britain's elected leader, involve the selection of candidates by party members, rather than the wider public. The result may easily be a candidate who appeals to the most committed voters but not to the independent, or swing, voters who decide the election. Old-style party elites, who had been through a few election cycles, probably had a better idea of which candidates would appeal to the public. They may also have had a better sense of whether the candidates, in private, have the same personalities as they present in public; Mr Cruz's inability to unite the anti-Trump forces clearly owed something to the fact that party leaders (such as John Boehner) dislike him so much.

There are moments in history, of course, when the old political and economic consensus breaks down, and a new world view emerges. The 1932 presidential election is a good example when the activist approach of Franklin Roosevelt swept aside traditional small government Republicanism or the 1979-1981 period when the conservative free-market Margaret Thatcher and Ronald Reagan came to power. But these moments tend to be preceded by a change in intellectual thought; it is not so much that experts are swept aside but that new experts replace the old. There is no sign that Donald Trump is drawing on any intellectual tradition at all; no groundswell of research arguing for building walls, deporting migrants or trade wars with China. A conservative thintank, for example, finds that his deportation plan would knock 2% off GDP; his combimnation of tax cuts for the rich and tariffs (higher prices on imported goods bought by the poor) would widen the inequality that many of his supporters are concerned about.

Indeed, this is the big worry for the economy, and for investors, when it comes to November's election. Some may feel that Trump the President will do none (or few) of the things that Trump the candidate has proposed. But of course that means we have no idea what he will actually do, and uncertainty tends to be what unsettles markets most. On that basis, the only thing we have to go on is the candidate's temperament, and here the bullying, the insults and his willingness to spread conspiracy theories are all very worrying. Political leaders are endlessly tested by "events, dear boy, events" as Harold MacMillan remarked; if their instant reaction is based on emotion, rather than reason, that should worry us all.

Congress and the Supreme Court may block some of Mr Trump's domestic policies (although his tax cuts will probably get through). Presidents have more scope when it comes to foreign policy which is not reassuring. Again, his electoral appeal seems to be linked to the idea that he will be "tough", except when it comes to Russia's Putin with whom he will cut a deal. This looks like a dangerous combination. A free hand to Mr Putin in eastern Europe could lead to all sorts of mischief in former Soviet states, and the weakening of the western alliance. And acting tough sounds good but if the other side's leaders have the same approach, tensions can quickly escalate. China's leaders have a nationalistic public to appease; they will not retreat if a trade war starts.

In this sense, Mr Trump is symptomatic of the rise across Europe of more nationalistic politicians; in Hungary and Poland, they have come into power. A shift from "love thy neighbour" to "loathe thy neighbour" makes international cooperation more difficult. But international cooperation is essential for tackling all kinds of problems from tax evasion though migration to terrorism. Such deals can only be reached if leaders compromise. But if leaders like Mr Trump see compromise as a sign of weakness (and encourage voters to think the same) deals will be impossible. That will make action impossible, ensuring global problems only get worse, and adding to the sense of public fury at the incompetence of the elites; a vicious circle.

Trust, compromise, reason—these are the elements that allow societies to function and have allowed, since 1800, what Deirdre McCloskey calls "the Great Enrichment" to occur. Belief that one man's hunches and facts plucked from the internet will provide a coherent alternative is the most irrational approach of all. Investors, who should be rational beings, ought to be very concerned.