Every US president since Jimmy Carter has spoken earnestly of the need to wean America from “foreign oil,” which is often more bluntly called “Middle East oil.” After the September 11, 2001 attacks and the resulting spotlight on Saudi Arabia, the clamor grew, only to subside, and now has resurfaced with the deepening cold war between the West and Iran. As part of their posturing on Iran, today’s GOP presidential candidates trip over themselves to pledge more drilling and exploration in the good ol’ US of A.

Media-certified deep thinker Newt Gingrich, for example, says such a “national American energy policy” would “allow us to be free in the Middle East, to not worry about [oil from] the Straits of Hormuz.”

There is frequent confusion about why the United States is so concerned with the flow of Persian Gulf oil, despite the best efforts of Michael Klare and others before him to explain.

One often hears it said, for example, that today the US imports more oil from Canada than from Saudi Arabia. Indeed, in September 2011, the US brought in 2,384 barrels per day from Canada and just 2,085 from all four Gulf countries (Saudi Arabia, Iraq, Kuwait and Oman) on the list of the top 15 sources. Mexico, Venezuela and Nigeria all outrank Iraq, and Iran is absent from the list. Why covet “their” oil if “we” do not need it?

Because the facts about current suppliers are irrelevant in the long term. Though Big Oil certainly is working to locate more major finds, the long-standing industrial consensus is that all of the non-Gulf oilfields (however big they are now) will be tapped out sooner than the Gulf’s, especially the gargantuan pools the Saudis are sitting on. More important than where “our” oil comes from, however, is the outward flow itself.

Oil, and particularly Persian Gulf oil, is the strategic commodity in the world. It makes everything run. And pending progress like invention of a cheap, high-performance electric car, or utter global calamity, oil will remain absolutely crucial until it is exhausted. In the meantime, the supply of Gulf oil to the world economy is vital -- and, for the political and technocratic classes in world capitals, being able to plan on its continued supply (ideally, at artificially low prices) is a cornerstone of grand strategy. As is the containment and, if need be, preemption of any local or global power that might have other plans.

For Washington mandarins of both parties and most ideological persuasions, the post-1970 US “forward-leaning posture” in the Gulf is likewise a main prop of that greatly cherished sole superpower status, for the US military essentially protects the oil patch on behalf of the rest of the world.

Neo-connish sorts will come out and say so, sort of. Thomas Donnelly of the American Enterprise Institute wrote in 2004 that a nuclear-armed Iran would be dangerous not because it posed an offensive threat, but “because of the constraining effect it threatens to impose upon US strategy for the greater Middle East. The danger is that Iran will ‘extend’ its deterrence...to a variety of states and other actors throughout the region.” To translate: One problem is that, with a bomb, Iran could deter the West from doing what was necessary to secure the flow of oil, should, for instance, the Strait of Hormuz chokepoint be threatened with closure.

Other species of policy intellectual, not to speak of politicians, are far more circumspect, confining themselves to vague (but always noddingly accepted) talk of “our interests in the region” if they do not pander to uninformed nativism à la Gingrich. But their calculations are basically the same. Another charter member of the GOP’s brain trust, Dick Cheney, convened a rather famous task force in May 2001 that concluded (pdf): “By 2020, Gulf oil producers are projected to supply between 54 and 67 percent of the world’s oil. Thus, the global economy will almost certainly continue to depend on the supply of oil from Organization of Petroleum Exporting Countries (OPEC) members, particularly in the Gulf. This region will remain vital to US interests.”

In today’s political atmosphere, the facts about where the US gets its oil now function primarily to normalize Iran war talk, as they downplay the direct costs to Americans of disruptions in the Persian Gulf oil supply. The point for those willing to entertain the war or air strike options is that disruptions would be temporary, while regime change in Iran would theoretically remove the threat of disruption over the long haul.

Too bad John Hodgman long ago cornered this phrase, because it would look good right here.

Update: Michael Klare has a good new piece that covers the bases.