As happens every few years, people who want to be elected president are out there promising me that I will receive huge benefits if I just pull the right lever next November.

Consider the current quartet of Republicans squabbling over convention delegates. Newt Gingrich, for example, promises that he will bring the price of gasoline down to $2.50 per gallon. All it will take, according to Mr. G, is increasing production here at home so we don’t have to import oil any more. According to the old law of supply and demand, he says, the increased supply will just naturally bring down the price of gas.

Unfortunately, Mr. G.’s theory leaves out 75 percent of that law. Sure, more supply tends to force prices down, but the lower prices will also lead people to buy more gas, which will tend to push the price back up. Not only that, if prices fall too low, producers might cut their production, reducing supply, which will also push prices up.

A couple of other realities argue against Gingrich’s theory as well. For one thing, there currently is no shortage of oil on the market in the U.S. In fact, in recent months, we’ve been exporting gasoline. And no matter where the oil comes from, it will go on the world market, and it’s that market that will determine the price. With oil consumption rising around the world, the pressure on oil prices will continue to go up. So much for $2.50 gas.

Mitt Romney’s promises are a bit different. He just promises that his election will bring instant improvement. Among other things, he has promised to repeal the health care reform Congress passed three years ago as soon as he takes his hand off the Bible on Inauguration Day. Since repealing acts of Congress unilaterally isn’t one of the president’s constitutional powers, I’m pretty sure that won’t happen. He may, of course, be able to take some actions that will inhibit the implication of the law over time, but that isn’t going to happen on Jan. 20.

Mr. R. might also find it difficult to keep his promise to run the government like he used to run his old investment firm. I once heard former Wyoming Gov. Stan Hathaway say that he intended to run the state government like a business, but upon taking office he quickly learned that government isn’t a business. A business, after all, has only one real objective, to make a profit. Making a profit isn’t the object of government, and the CEO of a business such as Romney’s has much more control over his firm than the president of the United States has over the federal government. Add the sheer size of the government and all its responsibilities, and it’s quite unlikely Mr. Romney will have the same success he did with his business.

Rick Santorum and Ron Paul have promised, each in his own way, to turn back the clock. Ron Paul promises everything will be better if the government returns to his strict interpretation of the Constitution, ending the Federal Reserve, for example. He apparently thinks it would be a simple matter to reverse more than two centuries of court rulings and precedents and apply 18th-century thinking to 21st-century problems. I think he’ll find it impossible to achieve his aims.

Santorum’s promise is a bit different. If he is elected, he will restore “traditional family values” to America, presumably because he has superior family values himself. Well, the concept of family values has been steadily evolving during my lifetime, and I’m not sure just what the president can do to reverse the trend except preach. And preaching about it might turn off a lot of the conservatives he’s trying to win over. Consider that conservatives have been grumbling about Michelle Obama’s suggestions that people need to adopt healthier diets for their children, that leads me to believe they would come unglued at a president who was preaching against something as private as people’s approach to their families.

Well, whether any of these guys ever actually get a chance to fulfill their dreams as president still is up in the air, but if one of them does, I’m pretty sure things won’t turn out quite the way he pictures them now. I suspect our three living former presidents as well as the current one will agree with me.

Reality has a way of interfering with fantasies.