Foreign policy does not determine American elections. Indeed, of all Western countries, we are the least interested in the subject. The reason is simple: We haven’t had to be. Our instinctive isolationism derives from our geographic exceptionalism. As Bismarck once explained (it is said), the United States is the most fortunate of all Great Powers, bordered on two sides by weak neighbors and on the other two by fish.

Two world wars, nuclear missiles and international terrorism have disabused us of the illusion of safety-by-isolation. You wouldn’t know it, though, from the Democratic presidential race where foreign policy has been treated as a nuisance, a distraction from such fundamental questions as whether $12 or $15 is the proper minimum wage.

On the Republican side, however, foreign policy has been the subject of furious debate. To which Donald Trump has contributed significantly, much of it off-the-cuff, contradictory and confused. Hence his foreign policy speech on Wednesday. It was meant to make him appear consistent, serious and presidential.

He did check off the required box — delivering a “major address” to a serious foreign policy outfit, the Center for the National Interest (once known as the Nixon Center). As such, it fulfilled a political need.

As did its major theme, announced right at the top: America First. Classically populist and invariably popular, it is nonetheless quite fraught. On the one hand, it can be meaningless — isn’t every president trying to advance American interests? Surely Truman didn’t enter the Korean War for the sake of Koreans, but from the conviction that intervention was essential for American security.

On the other hand, America First does have a history. In 1940, when Britain was fighting for its life and Churchill was begging for U.S. help, it was the name of the group most virulently opposed to U.S. intervention. It disbanded — totally discredited — four days after Pearl Harbor.

The irony is that while President Obama would never use the term, it is the underlying theme of his foreign policy — which Trump constantly denounces as a series of disasters. Obama, like Trump, is animated by the view that we are overextended and overinvested abroad. “The nation that I’m most interested in building is our own,” declared Obama in his December 2009 West Point address on Afghanistan.

This is also the theme of Bernie Sanders. No great surprise. Left and right isolationism have found common cause since the 1930s. Socialist Party leader Norman Thomas often shared the platform with Charles Lindbergh at America First rallies.

Both the left and right have a long history of advocating American retreat and retrenchment. The difference is that liberals want to come home because they think we are not good enough for the world. Conservatives want to wash their hands of the world because they think the world is not good enough for us.

For Obama, we are morally unworthy to act as world hegemon. Our hands are not clean. He’s gone abroad confessing our various sins — everything from the Iranian coup of 1953 to our unkind treatment of Castro’s Cuba to the ultimate blot, Hiroshima, a penitential visit to which Obama is currently considering.

Trump would be rightly appalled by such a self-indicting trip. His foreign policy stems from a proud nationalism that believes that these recalcitrant tribes and nations are unworthy of American expenditures of blood and treasure.

This has been the underlying view of conservative isolationism from Lindbergh through Pat Buchanan through Rand Paul. It is not without its attractions. Trump’s version, however, is inconsistent and often contradictory. After all, he pledged to bring stability to the Middle East. How do you do that without presence, risk and expenditures (financial and military)? He attacked Obama for letting Iran become a “great power.” But doesn’t resisting that automatically imply engagement?

More incoherent still is Trump’s insistence on being unpredictable. An asset perhaps in real estate deals, but in a Hobbesian world American allies rely on American consistency, often as a matter of life or death. Yet Trump excoriated the Obama-Clinton foreign policy for losing the trust of our allies precisely because of its capriciousness. The tilt toward Iran. The red line in Syria. Canceling the East European missile defense. Abandoning Hosni Mubarak.

Trump’s scripted, telepromptered speech was intended to finally clarify his foreign policy. It produced instead a jumble. The basic principle seems to be this: Continue the inexorable Obama-Clinton retreat, though for reasons of national self-interest, rather than of national self-doubt. And except when, with studied inconsistency, he decides otherwise.

© 2016, The Washington Post Writers Group