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Warren Buffet has long dabbled in politics. In the mid-1970s he developed a taste for exclusive Washington dinner parties. In the 1980s he spent a weekend being Ronald Reagan’s golf partner. He helped Arnold Schwarzenegger become the governor of California in 2003 and in 2008 John McCain and Barack Obama both hinted that they would like Mr. Buffett to become their Treasury secretary.
   This year America’s most famous investor has spoken out loudly on political affairs — aged a liberating 85 and with a left leaning credo. The latest of his annual letters to investors, which usually confine themselves to folksy jokes and dissections of insurers’ reserve ratios, has a passionate repudiation of the bleak national mood. "For 240 years it’s been a terrible mistake to bet against America," it declares. On August 1st Mr. Buffett was on stage with Hillary Clinton in Omaha and laid into Donald Trump’s character and business record.
   If the intensity of Mr. Buffett’s interventions has risen over time, so has the seriousness with which they are taken. This partly reflects his financial clout. Berkshire Hathaway, his investment vehicle, is worth $363 billion and is the world’s sixth-most valuable firm. He is at least 20 times richer than Mr. Trump. It also reflects Mr. Buffett’s popularity: 40, 000 people attended Berkshire’s annual meeting in April, compared to 5, 000 two decades ago. Since the death of Steve Jobs, the boss of Apple, Mr. Buffett has become the lone hero of big business in America. He stands for the promise of a nostalgic, fairer kind of capitalism.