H L Mencken based his journalistic career on the proposition that public officials in a democracy "were predominantly frauds and hence did not deserve to be taken seriously", except in their potential for criminally irresponsible behaviour. Mencken's faults are well known - the worst of them being his anti-Semitism - but the combination of his literary talent, his anti-democratic temper and his iconoclastic impulses made him a political critic without peer in the first half of the 20th century.

Nor have there been many more effective scourges of reaction in the United States, particularly in the South, than this gifted reactionary. As a new biography reminds us, although there are commentators on both sides of the Atlantic today who display some of both his vices and his virtues, there is nobody with quite his capacity for puncturing the pretensions of the powerful and overturning the received wisdom of the day. Sometimes resoundingly right and equally, or even more often, resoundingly wrong, he was particularly good on politicians who take their countries into wars. He rose magnificently above both political correctness and political incorrectness.

Mencken once reduced a British diplomat to glassy-eyed silence at a dinner by arguing that the US had "gone into the first world war on the wrong side - that it would have got more out of the business, and at much less cost, if it had ganged up with Germany against England, and so ensured a German victory and a fat share of the loot."

Mencken did not like things British, including the food, which even at its best he described as "to the windward side of indifferent", or the empire, "grounded upon a preposterous series of frauds", or even the Manchester Guardian, with which his own paper, The Baltimore Sun, had at one time a close connection.

Alone among his Baltimore colleagues, who found much to admire during trips to Manchester in the 30s, Mencken - while noting as an aside that Mrs Ted Scott's kitchen had no refrigerator - concluded that the "Guardian brethren... got out a very poor paper. There was very little spot news in it, and most of its so-called correspondence was so obviously biased that it was of little value."

He reserved his greatest scorn for American presidents of both parties. Woodrow Wilson was a man whose speeches transcended "mere mendacity"; Herbert Hoover bribed his way to the nomination at a convention where "the knavish dishonesty of politicians" had never "been more dramatically displayed"; while Franklin Roosevelt was a demagogue and a sorcerer. George W Bush might take some comfort from Mencken's view that a man of limited talents could handle the presidency. "I don't believe the presidency requires genius. If it did, we'd have gone the way of Sodom and Gomorrah long ago. All the job needs is the sound, homely, enduring competence that one looks for in the better sort of college president, newspaper city editor, or saloon keeper."

A drinking man throughout his life, Mencken was present during the heavy session at a Baltimore dining club where the song "I am 100 Percent American, Goddamn!" was created. During prohibition, he tended to rate the party conventions on the basis of the availability of liquor rather than on their political achievements, reserving great praise for the San Francisco mayor who supplied 50 barrels of Bourbon, paying for it out of the fund for the city's smallpox hospital.

The Kaiser in exile read Mencken's Notes on Democracy, became a great fan, and sent autographed silver-framed photographs of himself to the Baltimore curmudgeon. "Until his death in 1941 he kept on whooping up my book," Mencken wrote, "as the leading authority on the crimes and imbecilities of democracy."

Mencken was indeed deeply disrespectful of democratic government, deeply disrespectful of those who proposed to reform government, and deeply disrespectful of the governed. In his last column for the Sun he wrote that "the credulity of the American people, whether in peace or war, has always been grossly underestimated even by those who charge it against them."

Mencken's creed was a hard one. He attacked politicians and their decisions, but never succumbed to the notion that the reformers waiting in the wings were necessarily any better, and never subscribed to the view that the people are superior to their leaders. But this universal dyspepsia sometimes enabled him to see very clearly what was going wrong in his and other societies. It would hardly do if everybody was like Menken, but we could do with more of his kind of sensibility today.

· The Sceptic by Terry Teachout (HarperCollins).
m.woollacott@theguardian.com