Battling my way through Sarah Palin's book, Going Rogue, last weekend, I began to wonder how American conservatism had come to this. Ms Palin's book is smug, lightweight, nationalistic, entirely free of original ideas. How has this woman become the darling of the American right? How has she become so popular that some bookmakers make her the favourite to win the Republican party nomination in 2012?

And then I realised – the rot set in with Ronald Reagan.

This might seem an odd conclusion, since President Reagan is a conservative hero who won two presidential elections. But the ideas that are now known as “Reaganism” are, in fact, profoundly subversive of some of the most important conservative values. Traditional conservatives disdain populism and respect knowledge. They believe in balancing the government's books. And they are pragmatists who are suspicious of ideology. Reagan debased all these ideas – and modern American conservatism is still suffering the consequences.

The most damaging idea propagated by the Reagan myth is the cult of the idiot-savant (the wise fool). You can see it in the very first line of Dinesh D'Souza's admiring biography of Reagan, which proclaims: “Sometimes it really helps to be a dummy.” Mr D'Souza recounts numerous stories in which intellectuals – even conservative intellectuals – disdained Reagan. They scorned his tendency to spend cabinet meetings sorting jelly beans into different colours, and his taste for flaky anecdotes. But, Mr D'Souza concludes, the “dummy” was right and the pointy-heads were wrong.

A dangerous chain of reasoning flows from this popular version of history. Reagan was apparently stupid and often startlingly ignorant – but he was vindicated by history. Therefore, goes the theory, ignorance and stupidity are good signs. They show that a politician is in tune with the deeper wisdom of the people. Once you start thinking like that, it is but a short step to Sarah Palin.

If it is ignorance you are after, then Ms Palin is definitely your woman. Game Change, a recent book on the 2008 presidential election campaign, recounts how desperate advisers to the McCain-Palin campaign decided that they had to give her a crash-course in modern history, before the vice-presidential debate with Joe Biden.

“They sat Palin down at a table in the suite, spread out a map of the world, and proceeded to give her a potted history of foreign policy. They started with the Spanish civil war, then moved on to world war one, world war two, the cold war . . . When the teachers suggested breaking for lunch or dinner, the student resisted. ‘No, no, no, let's keep going,' Ms Palin said. ‘This is awesome'.”

The history of the 20th century? I suppose it is pretty awesome.

In fact, Ms Palin is much, much less qualified to be president than Reagan ever was. She is Ronald Reagan lite – and Reagan was pretty lite to begin with. But he had, at least, been governor of California, not Alaska, and had read widely.

The damage Reaganism did to conservatism extends well beyond the Palin effect. The late president also became associated with a couple of bad ideas that helped make the administration of George W. Bush such a disaster. The first was fiscal incontinence; the second is the view that the key to a successful foreign policy is a rigid distinction between good and evil, and a strong military.

The Republican party – with Ms Palin to the fore – is currently decrying the huge deficits being run by the Obama administration. But this is a recent conversion. Ever since the Reagan years, the Republicans have been the party of deficit spending.