Donald Trump has wrecked the best plans of nearly a score of “serious” Republican presidential candidates. Yet what may be most extraordinary about his campaign is that on foreign policy, at least, he may be the most sensible Republican in the race. It is the “mainstream” and “acceptable” Republicans who are the most extreme, dangerous and unrealistic.

First, the Republicans scream that the world has never been so dangerous. Yet when in history has a country been as secure as America from existential and even substantial threats?

Hyperbole is Trump’s stock in trade, but he has used it only sparingly on foreign policy. Referring to North Korea, for instance, he claimed: “This world is just blowing up around us.” But he used that as a justification for talking to North Korea, not going to war.

Second, the Republicans generally refuse to criticize President George W. Bush’s misadventure in Iraq. In contrast, the Donald said “I was not a fan of going to Iraq.” He asked how someone like Florida Sen. Marco Rubio is “going to lead us” if he can’t say where he stands on such an issue.

Third, the Republican candidates blame the rise of the Islamic State, also known as ISIS, on Barack Obama. This claim is false at every level. The Islamic State grew out of the Iraq invasion and succeeded with the aid of former Baathists and Sunni tribes which came to prefer an Islamist Dark Age to murderous Shiite rule. There were no U.S. troops in Iraq because Bush failed to win agreement from Baghdad.

Trump understands that the basic mistake was invading Iraq. He said: “They went into Iraq. They destabilized the Middle East. It was a big mistake. OK, now we’re there. And you have ISIS. And I said this was going to happen.”

Fourth, in general the Republicans believe in having to fight throughout the Middle East. There is support for sending U.S. forces to Iraq, Syria and Yemen, without the slightest showing of vital American interests being at stake.

Against Islamic State, Trump also recently advocated “boots on the ground,” but for a unique purpose: “I said you take away their wealth, that you go and knock the hell out of the oil, take back the oil.” And at least he hasn’t advocated warring in Syria or Yemen.

Fifth, Republicans see other waiting enemies, such as China. But Trump apparently doesn’t view war as an option against Beijing. Rather, he sees China primarily as an economic competitor: He declared that he would “get tough with” and “out-negotiate” the Chinese, not bomb them.

Sixth, all the other Republicans, including Kentucky Sen. Rand Paul, apparently view Iran as an unspeakable enemy. All would block the Obama nuclear deal and most appear ready to tear it up.

Trump criticized the agreement, but announced: “I will police that deal. You know, I’ve taken over some bad contracts. … I would police that contract so tough that they don’t have a chance.”

Seventh, the GOP candidates almost uniformly treat handing out security guarantees as similar to accumulating Facebook friends: The more the merrier.

Yet most of America’s major allies can defend themselves. The Europeans, for instance, have a combined population and GDP greater than America and much greater than Russia. South Korea has twice the population and around 40 times the GDP of the North.

Some potential allies are security black holes, such as Ukraine. It would set the U.S. against nuclear-armed Russia. America has nothing at stake warranting that kind of risky confrontation.

Many of America’s official friends are more oppressive than Washington’s enemies. Saudi Arabia, for instance, is a totalitarian state. Egypt today is more repressive than under Mubarak.

Here Trump is at his refreshing best. Decades ago he called on the U.S. to “stop paying to defend countries that can afford to defend themselves.” He then pointed to Japan and Saudi Arabia. Today only Trump asks why U.S. politicians have turned these and other allies into welfare dependents.

For instance, a couple years ago he said: “I keep asking, how long will we go on defending South Korea from North Korea without payment?” Similarly, Trump explained: “Pulling back from Europe would save this country millions of dollars annually. The cost of stationing NATO troops in Europe is enormous.” Regarding Ukraine, he asked: “Where’s Germany? Where are the countries of Europe?”

Trump obviously is not a deep thinker on foreign policy or anything else. Nevertheless, on these issues he exhibits a degree of common sense lacked by virtually every other Republican candidate. The Republican Party needs to have a serious debate over foreign policy.

Doug Bandow is a senior fellow at the Cato Institute and a former special assistant to President Ronald Reagan. He is the author of “Foreign Follies: America’s New Global Empire” (Xulon).