ANALYSIS: After a tragic week in the United States, the main actor in the presidential election has been Donald Trump, but for all the wrong reasons.

Photo: AFP

Donald Trump promised that once selected he would reinvent himself into a kinder, gentler candidate with a more presidential demeanour. It lasted a single speech. The moment Mr Trump goes off script he reverts to type, revelling in the attention he derives from scurrilous and swingeing attacks.

Historian Tom Holland has drawn parallels between Mr Trump and the Roman Emperor Caligula.

Not so much for the orgies (so far as we know), but for the conscious populism - tapping into the people's feelings about the elite, drawing on the energy of the mob, the taste for spectacle.

Caligula's ultimate downfall was his liking for humiliation and his inability to self-censor. He compared a Praetorian Guard's voice to a girl's and discovered the soldier's sword was sharper than his tongue. Which is somewhat reminiscent of Mr Trump's mocking of disabled journalist Serge Kovaleski, give or take a sword.

Photo: AFP

A lack of impulse control and a penchant for populist bigotry is a dangerous mix in a politician, especially with a dollop of conspiracy theory. It makes for a career sometimes entertaining, frequently horrifying, but not often long-lived. Except when the ground conditions are just right, but more on that in a moment.

Firstly, is it reasonable to call Mr Trump for bigotry?

A potted history may be useful. In the 1960's Richard Nixon's strategists concocted the Southern Strategy. The aim was to capture the American South from the Democratic party by appealing to white southern racist anger over the advances of the civil rights movement. The 1964 rout of Barry Goldwater, who was considered dangerously intemperate, demonstrated that unguarded speech scares the moderates, so the bigotry went underground and the southern strategy was achieved through coded language referred to as Dog Whistle Politics.

For example, calling for 'states rights' meant segregating blacks if you want to, and now means banning gays, abortion and Muslims if you want to.

'Inner city crime' is code for blacks are criminals, and 'Barack Hussein Obama' means he's really a secret Muslim foreigner, (can you remember any other recent candidate's middle name?)

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The In-his-own-words Trump Bigotry Checklist:

As Republican dirty-tricks specialist Lee Atwater explained: "By 1968 you can't say "nigger" - that hurts you. Backfires. So you say stuff like forced busing, states' rights and all that stuff."

The Southern Strategy worked, and the south is now the fortress of Abraham Lincoln's Republican Party. Both Abraham Lincoln and Jefferson Davis are spinning in their graves (in opposite directions). However, the cynical racism also created a monster that has become hard to manage, and as demographics have shifted and Latino and Black populations in the south have burgeoned, the southern strategy has become a curse, making it increasingly difficult for the Republicans to win the Presidency.

After the 2012 election the Republican Party commissioned a surprisingly frank review of what had gone wrong.

It noted that: Minorities now make up 37 percent of the population and Mr Obama won 80 percent of the non-white vote. If the GOP continues to repel the non-white vote they force themselves to try to win impossible proportions of the white vote to make up the difference. Basically, angry old white men aren't a majority anymore so bigotry is a bad strategy. Tea-Party leader, Dick Armey, told the investigators, "You can't call someone ugly and expect them to go to the prom with you." The Donald has obviously not read the memo.

Photo: AFP

The problem is that the Grand Old Party has been the natural home of racism, bigotry and anger for so long now that for many of the core voters it just doesn't seem wrong anymore.

Mr Trump has been soaking in it and so have his natural constituency. He isn't saying much that Republican politicians haven't said in code for decades, he just left the dog whistle at home and now everyone can hear it.

This is part of what makes him sound 'honest', but it's anathema out loud, even to his own party leaders - let alone moderates or independents. Even the very partisan Republican Senator Lindsay Graham called him "a race-baiting, xenophobic, religious bigot".

Donald Trump is systematically alienating each of the very groups the Republican Party decided were essential to it having any chance of winning.

There are times when out and out xenophobia can work for politicians, despicable and dangerous as it is. The Brexit campaign shows that the fear of immigrants will lead people to vote against their own economic interests. But such fear and blame politics only works on enough voters if the national woes (especially economic woes), are dire enough that voters need someone easy and "other" to blame.

And there's the rub for Mr Trump. Because, whilst Europe's lurch into austerity caused an economic depression in Britain that has made life dreadful for many, in America Mr Obama's opposite policy insulated the economy from the worst aftereffects of the 2008 recession.

As a result the population are not poor enough, weary enough or scared enough for Mr Trump's tactic to work and the more forcefully bigoted and absurd his statements become, the more evident the divide will come between them in in the polls.

Like Caligula, an intemperate tongue will be his downfall.

* Phil Smith is an RNZ journalist who has wasted his adult life revelling in the entertaining minutiae of American politics and culture. He once shared a lunch of rare bison steaks with Jimmy Carter.