The chairman of Berkshire Hathaway, Warren Buffett, has gained a lot of attention for his backing of the presidential campaigns of Senators Obama and Clinton. Mr. Obama is fond of quoting Mr. Buffett on the injustice of chief executives paying lower tax rates than their secretaries, because of the way the cap on the annual income that is subject to the Social Security payroll tax counteracts the progressive rate structure of the federal income tax. Mr. Buffett’s support for the death tax is a staple of left-wing editorial columns.

So it will be illuminating to see whether the same amount of attention attaches to the warning in respect of trade that Mr. Buffett included in his annual letter to his shareholders, which was released over the weekend. “In developing a sensible trade policy, the U.S. should not single out countries to punish or industries to protect. Nor should we take actions likely to evoke retaliatory behavior that will reduce America’s exports, true trade that benefits both our country and the rest of the world,” the Sage of Omaha wrote. In an appearance yesterday on CNBC, he expanded on the point. “I believe in free trade. In fact, I would have no barriers to countries or products or anything of the sort,” he said, adding of Mr. Obama and Mrs. Clinton, “I’m not going to get too specific on the eve of the election tomorrow, whether or not I agree with them. I will say this, I don’t agree with them on everything.”

Well there’s an understatement. Mr. Buffett’s advice on trade is exactly the opposite of the Nafta-bashing message that the billionaire’s preferred presidential candidates, Mr. Obama and Mrs. Clinton, have been offering to the voters of Ohio. It’s more in line with the pro-Nafta message that Mr. Obama’s economic aides have been assuring Canada he will hew once the primary season is over, and with the pro-Nafta message on which President Clinton rode to re-election in 1996. But on the record, Mr. Obama and Mrs. Clinton are on this issue singing from a different hymnal than Mr. Buffett.

While we are on the subject of the Sage’s sageness, how about his announcement that Berkshire Hathaway had sold its $4 billion holding in PetroChina? Less than a year ago, Mr. Buffett was urging his shareholders to vote “no” on a proposal for Berkshire to sell its PetroChina stake. The proposal was brought by those concerned about the role of PetroChina’s parent, China National Petroleum Corporation, in Sudan, whose government is complicit in the genocide in Darfur. The Berkshire Hathaway shareholders indeed, by an overwhelming margin, rejected the divestment proposal.

In his chairman’s letter, Mr. Buffett explained the sale in economic terms — “the market value of the company rose to $275 billion, about what we thought it was worth compared to other giant oil companies” — without mentioning the Sudan issue at all. That explanation doesn’t square with his previous statements that his ideal holding period for a stock is “forever,” or with his disavowal of target prices — “I’ve never had a target price or a target holding period on a stock,” Businessweek once quoted Mr. Buffett as saying.

Readers of these columns may recall our April 5, 2005 editorial, “Harvard and PetroChina,” marking Harvard University’s decision to divest. PetroChina’s value more than doubled between when Harvard sold and when Mr. Buffett did, making clear that conscience has its costs. Another topic, along with trade and taxes, for Mrs. Clinton and Mr. Obama to raise with the Sage of Omaha at the next campaign fundraiser for them at which he serves as the star attraction.