If we want to start worrying about the effect this American midterm election might have on Israel, there is one piece of history we might want to keep in mind.

When we undertook the war in Iraq, a large majority of Americans said it was a good idea. Now, a large majority says it was a bad idea. About the same large majority of Americans thought the Korean War was a good idea when President Truman initiated it, and, after a few years, a large majority thought it had been a bad idea. When we undertook the Vietnam War, a large majority of Americans said that it was a good idea. A few years later, a large majority thought it had been a bad idea.

Both of those wars, Korea and Vietnam, had gone badly. We had expected early victories, but instead, we got a lot of expensive deadlock, high casualty rates and much criticism of the way in which each war had been conducted. Sound familiar? In the end, we did prevent a takeover of South Korea, but it could not be said that we “won” that war — and we did not even prevent a takeover in the Vietnam War.

Both wars, Korea and Vietnam, might be seen as major battles in the so-called Cold War, undertaken in the name of our effort to contain the expansionist ambitions of the Soviet Union — by force, if necessary. The American people came to feel that this overarching purpose had been badly served because those two wars had been either wrongly undertaken or badly conducted, or both.

However, the American people continued to support the efforts by administrations of both political parties to contain the Soviet Union — by force if necessary. After the Korean War fiasco, they supported President Kennedy’s threat to go to war against a proposed Soviet rocket base in Cuba, and they initially supported the military build-up by Presidents Eisenhower and Kennedy in Vietnam. After the Vietnam War fiasco, they supported President Reagan’s military buildup against the Soviet Union.

In short, the public continued to support the overarching purpose of the sub-wars that in practice they had come to reject — and that large purpose was the basis of a clearly understood foreign policy. But today, unlike that earlier history, after rejecting the war in Iraq the American people are left with no overarching foreign policy at all. That policy void is one of the failures of political leadership that led to the results of the last election — and that lack of a cogent foreign policy leaves Israel, among others, in harm’s way. We lost an opportunity to make clear the threat that faces America, the West and — most imminently — Israel.

After all, guaranteeing Israel’s security is not and has never been the centerpiece that drives American foreign policy. That guarantee will be in effect only if there is an overall policy in which Israel plays an important part. Protecting Israel became indispensable only when its importance to America’s Cold War strategy became apparent, largely after 1967.

Of course, Israel’s stability and alliance in the Middle East is still of some strategic importance to America. America’s foreign policy rode along on that — and on a similarly vague belief that a democratic world is good for America. But remember that most Americans are not foreign policy wonks. They have foreign policy passions only when a very discernible threat to their country is perceived. (And remember that in all the surveys showing how many more Americans think this country should favor Israel rather than the Arabs, about half of the total population usually has no opinion, or thinks the U.S. should be neutral).

But since the midterm elections, what is the threat around which a passionate foreign policy can be built for the American people?

Isolationism is not a viable alternative in the modern world. The elimination of stateless terrorists will continue to be seen as a serious law enforcement problem, not as the basis of a compelling foreign policy. As the bipartisan commission to investigate 9/11 stated, “the problem is that [the terrorists] represent an ideological movement, not a finite group of people” — an ideology identified by that commission as the radical Islamist movement in the Middle East.

But the midterm election emphasized the failure of our leadership to articulate the nature of that threat, and/or run a war to address it. So for the first time in almost a century, we have no overarching foreign policy — and we need one urgently. It is now necessary for a divided political leadership to overcome bipartisanship and cobble a cogent foreign policy together to meet that overarching threat. If they don’t, America — along with the world, and especially Israel — will be in trouble.

Earl Raab is director emeritus of Brandeis University’s Nathan Perlmutter Institute for Jewish Advocacy, and executive director emeritus of the S.F.-based Jewish Community Relations Council.