Looking at Nigel Farage posing like a movie gangster in a publicity photo for his American trip – the cosy pint he affects for British audiences replaced by a macho cigar – I found myself thinking of Bertolt Brecht’s play The Resistible Rise of Arturo Ui. In his 1941 satire on the far, far right, Brecht portrays Adolf Hitler as a Chicago mobster whose thuggish rise to power is made possible by his enemies’ weakness – his rise was “resistible”.

Farage is not Hitler, of course – I would not dream of giving him that much historical significance – but he looks a hell of a lot like Arturo Ui in this photograph. It appears on publicity material in the US, where he has gone down like a stormtrooper – sorry, a storm! – at a conservative Republican rally with his ramped-up rhetoric about the west’s “Judeo-Christian values” being undermined by an Islamist “fifth column”.

The only fifth column that I can see that is seriously menacing decent British values of tolerance and kindness is Ukip, with its increasingly audible background drums of hate.

American republicans apparently believe he may “run Britain”. It is easy to laugh at that idea from this side of the Atlantic. Here in the UK the liberal consensus appears still to be that, despite a poll predicting that Farage will win a seat in the general election, he and Ukip are marginal, even declining forces on the national stage – and perhaps even a Good Thing if they undermine Cameron and let Labour form a government.

But we should pay heed to the American view of Farage. And we should be scared by this photograph. This is a picture of a dangerous man.

It is as if, to impress the Yanks, Farage has unveiled his inner gangster: the street fighter, the Machiavellian bastard, showing his arrogance and thuggishness.

It is very risky to underestimate a politician who has successfully created a seat-winning British party to the right of the Conservatives. That phrase makes me shudder. To the right of the Conservatives. Such a force is a grotesque thing to have within our democracy – a deeply un-British virus, a cancer.

Like Arturo Ui or Richard III, he wears the right mask for the occasion. A normal guy, a nasty guy – whatever it takes

Brecht’s Arturo Ui is not only Hitler: he is Richard III. Brecht’s play is an update of Shakespeare’s study of power. The point about Shakespeare’s Richard III is that he is ill-favoured, with apparently no chance of becoming king. He does it through audacity, brutal cynicism and brazen fraud. Shakespeare was influenced by the political writings of Niccolò Machiavelli. Richard is a “Machiavel”, a ruthless political player. This photograph reveals that Farage too is a true Machiavellian.

The revelation here is what fools he makes of us all. In Britain he assiduously maintains the image of an ordinary bloke, down the pub, always with a joke. Now here he is in America deliberately showing a totally different face. Perhaps it is the real him, the beer hall – sorry, conference hall – rabble rouser. And maybe it is also a confession of his total fakery. Like Arturo Ui or Richard III, he wears the right mask for the occasion. A normal guy, a nasty guy – whatever it takes. Farage is an utterly ruthless performer, and anyone who underestimates his threat to British decency is a fool.

The rise of Arturo Ui was resistible. Brecht would have applauded the protesters who made a fool of Farage when they wrecked his horrible attempt to make political capital in Rotherham. The way to fight Farage is with street protests, demonstrations, cartoons, insults – and any political weapon that comes to hand.