Here’s a word you can expect to hear quite a bit between now and the 2012 election: speculators.

The way President Obama has been using the word recently, it means, “the guys — not me! — who made your gas prices go up.”

In a speech over the weekend, Mr. Obama put it this way: “we’ve launched a task force led by the Attorney General that has one job: rooting out cases of fraud or manipulation in the markets that might affect gas prices, including any illegal activity by traders and speculators.”

The president has also used the word recently in less formal settings, like a town hall in Virginia: “The problem is, is that oil is sold on these world markets, and speculators and people make various bets…and that spikes up prices significantly.”

Back in 2009, Mr. Obama used the same term to mean “the guys — not me or the auto workers union — who deserve blame for Chrysler’s bankruptcy.” “It was unacceptable to let a small group of speculators endanger Chrysler’s future by refusing to sacrifice like everyone else,” he said.

Mr. Obama’s attacks on speculators struck me as a departure from presidential precedent. Thanks to the marvelous American Presidency Project of the University of California, Santa Barbara, it’s now easy to search for a word like “speculators” in the speeches of previous presidents.

The results are both sobering and illuminating. It turns out that American presidents have been warning about the danger of speculators all the way back to Thomas Jefferson, who in 1804 explained to the Senate a provision of treaty with the Creek Indians by writing, “instead of giving them stock which may be passed into other hands and render them the prey of speculators, an annuity shall be paid.”

Theodore Roosevelt spoke of the “proper desire to prevent” Puerto Rico and the Philippines from “being exploited by speculators.”

Franklin Roosevelt denounced “those reckless speculators with their own or other people’s money whose operations have injured the values of the farmers’ crops and the savings of the poor.”

John F. Kennedy justified a one-year threshold for preferential tax treatment on capital gains as a way of distinguishing between “bona fide investors” and “short-term speculators.”

Jimmy Carter accused Republicans of choosing as secretary of agriculture “some lawyer who represented grain speculators or other processors of food who bought grain and products from farmers cheap during harvest season, and then sold it to consumers high after they manipulated the market.”

Even President Reagan faulted Congressional Democrats for a bill he said would “offer 2,500 commodities speculators a tax break of some $400 million,” and he warned against intervention in the foreign exchange market, calling it “an exercise in futility that would probably enrich currency speculators at the expense of American taxpayers.”

For more than 200 years, in other words, presidents of all political parties have found “speculators” convenient scapegoats and targets.

Would it be too much to ask for a president who, rather than denouncing speculators, stands up for them? Such a politician might say something like, “Remember, risk-taking is part of capitalism. These traders are actually providing useful services by accepting risks from those who wish to offload them, by supplying liquidity in markets, and by sending price signals that carry valuable information.”

People who really grasp these concepts tend to go into private-sector work rather than government. But what a public service could be performed by a candidate who explains that speculators is just a word politicians use to describe entrepreneurs that the politicians don’t like.

Mr. Stoll, editor of FutureOfCapitalism.com, is the author of Samuel Adams: A Life.