This perspective is seen most clearly, perhaps, when pollsters presented Americans in 1993 with the statement, “Nothing the U.S. could accomplish in Somalia is worth the death of even one more U.S. soldier.” Fully 60 percent expressed agreement. This is not such an unusual position for humanitarian ventures. If Red Cross or other workers are killed while carrying out humanitarian missions, their organizations frequently threaten to withdraw, no matter how much good they may be doing.

Some commentators, including such unlikely soulmates as Andrew Bacevich, Robert Kagan, John Mearsheimer, Rachel Maddow and Vladimir Putin, have variously maintained that we have seen the rise of a new American militarism in the last decades or that Americans hail from Mars.

But that perspective extrapolates far too much from the wars in Afghanistan and Iraq. In these cases, opinion was impelled not by a propensity toward militarism, but, as with entry into World War II, by the reaction to a direct attack on the United States. These ventures—the 9/11 wars—have proved to be aberrations from usual patterns, not portents of the future. Although they demonstrate that Americans remain willing to strike back hard if attacked, they do not indicate a change in the public’s reticence about becoming militarily involved in other kinds of missions, particularly humanitarian ones.

An examination of the trends in a poll question designed to tap “isolationism” does not suggest a surge of militarism. Instead, it documents something of a rise in public wariness regarding military intervention beginning with the Vietnam War and, thereafter, a fair amount of steadiness punctured by spike‐​like ups and downs in response to current events, including 9/11 and its ensuing wars.

Since 1945, pollsters have periodically asked, “Do you think it will be best for the future of this country if we take an active part in world affairs, or if we stayed out of world affairs?” The question seems to have been framed to generate an “internationalist” response. In 1945, after all, the United States possessed something like half of the wealth of the world and therefore scarcely had an option about “taking an active part in world affairs,” as it was so blandly and unthreateningly presented. And, so queried, only 19 percent of poll respondents in 1945 picked the “stay out” or “isolationist” option. The authors of the poll question got the number they probably wanted.

(Actually, to generate high levels of this quality, the query can be reformulated to “We shouldn’t think so much in international terms but concentrate more on our own national problems and building up our strength and prosperity here at home.” In that rendering, measured “isolationism” registers 30 to 40 percentage points higher.)

In the post‐​war years the “stay out” percentage rose a bit to around 25 percent, but it had descended to 16 percent in 1965 in the aftermath of the 1962 Cuban missile crisis and as the war in Vietnam was about to begin. The experience of that war pushed it much higher—to 31 to 36 percent—as part of what has been called the “Vietnam syndrome.”

It has stayed at around that level ever since. There was a temporary downward dip during the Gulf War of 1991 and interesting spikes upward at the time of the Kosovo conflict in 1999 even though no American troops were lost and even though it was deemed successful at the time. And, in this century, the “stay out” percentage dropped to 14, its lowest recorded level, in the aftermath of 9/11. It rose the next year, and then plunged downward again in 2003 and 2004, the first two years of the Iraq War. By 2006, however, it had risen again to post‐​Vietnam levels where it has remained through 2012, the last time the question was asked.

Given the bland attractiveness of the “take an active part in world affairs” option, it is impressive that around a third or more of the public since Vietnam has generally rejected it to embrace the “stay out” option. However, this is likely to be more nearly an expression of wariness about costly and frustrating military entanglements than a serious yearning for full withdrawal. There is, for example, no real indication that Americans want to erect steely trade barriers. And polls, including ones on Syria, continually show that the public is far more likely to approve foreign ventures if they are approved and supported by allies and international organizations. Real isolationism should be made of sterner stuff.

The public response to intervention in Syria also suggests that people, contrary to a large literature, are not readily manipulable by “opinion elites.” The Obama administration dramatically proposed military action in response to chemical weapons use in Syria, and leaders of both parties in Congress rather quickly fell into line. Moreover, these bipartisan “leadership cues” were accompanied by disturbing photographs of the corpses of Syrian children apparently killed in the attack.

Nonetheless, the American public has been decidedly unwilling even to support the punitive bombing of Syria—a venture likely to risk few if any American lives—out of concern that it would lead to further involvement in the conflict there. And the U.S. public has remained suspicious of, and therefore immune to, repeated assurances from President Barack Obama that he has categorically ruled out putting “boots on the ground” in Syria.

Leaders may propose acting abroad, but that doesn’t mean public opinion will move in concert, that people will necessarily buy the message. And on the occasions when they do, it is probably best to conclude that the message has struck a responsive chord, rather than that the public has been manipulated.

Ideas are like commercial products. Some become embraced by the customers while most, no matter how well packaged or promoted, fail to ignite acceptance or even passing interest. It is a process that is extremely difficult to predict and even more difficult to manipulate.