My grandmother would have had a Yiddish word for Donald Trump’s “major” foreign policy speech last week: meshugaas. That means behavior so senseless or crazy it is almost incomprehensible.

Indeed, the Trump talk was so incoherent, so full of contradictions, that, in normal times, it would have been quickly relegated to the realm of late-night comics. But these aren’t normal times. As Trump moves within grasp of the GOP nomination, the dangers of Trumpism are no laughing matter.

For those who haven’t taken Trump’s demagoguery seriously enough until now, this speech should be a wakeup call. The idea that a man with his mindset might ever have his hand on the nuclear trigger is a very scary thought.

As his remarks made clear, Trump views the world through the prism that defines his entire campaign — the politics of grievance: America is going down the toilet. Everyone is dumping on us. Our allies don’t pay us enough and our enemies don’t respect us. We aren’t going to put up with it anymore.

The solution for everything, as he never ceases to remind us, can be found only in one venue, his own persona. “I’m the only one — believe me. I’m the only one who knows how to fix it,” the Donald proclaimed in his speech.

But that beggars belief, not least because he lies so often and so repeatedly, providing media fact-checking sites with endless fodder. Prime among his frequent falsehoods are the constant claims he was against George W. Bush’s Iraq war and President Barack Obama’s intervention in Libya. In reality he is on record as having supported the Iraq invasion, and pushed for U.S. intervention in Libya. He even suggested the Libyan opposition could pay the United States with oil funds once Moammar Gadhafi fell.

So what is the Trump Doctrine to stop the world from exploiting us? From his speech, and his previous foreign policy utterings, it appears to be a variant of isolationism, sort of, maybe. Just pull back and let ’em rot.

Trump is campaigning on the slogan of “America First” which — as has been widely noted — was the mantra of the pre-World War II, pro-Nazi isolationists who sought to keep the United States out of that war.

And, indeed, although he’s no anti-Semite, Trump makes clear he’d be willing to abandon NATO if the European allies don’t cough up more. In earlier remarks, he talked of pulling U.S. troops out of Japan and South Korea, and letting both of them go nuclear as America ceases to provide a nuclear umbrella.

He displays no comprehension of the value those alliances still provide to this country, or the dangers of American isolation in a world of new challenges. Nor does he appear to grasp the risks of Asian nuclear proliferation (even though he notes, without further explanation, that “the power of weaponry is the single biggest problem that we have today in the world”).

Indeed, the speech is such a crazy mashup of contradictions one can’t be certain what, if anything, Trump believes in. His aides busily whisper that he’d be more responsible when he took office. But, at this point, one must start judging Trump by what he says and how that reflects on the man.

He claims we need a long-term plan to halt radical Islam but presents none. Then he adds that he will “work very closely with Muslim allies” but talks of banning all Muslims from entering the country.

He shows a wariness of using American force abroad, and says he will only help nations “that are good to us” fight terrorism. But then he says that the Islamic State will be gone “very, very quickly, if I’m elected.” Perhaps he’s willing, as he has hinted in several interviews, to use “tactical nukes.”

Even as he threatens America’s allies, Trump says his administration will “lead a free world that is properly armed and funded beautifully.” Yet the foreign leader about whom he waxes most enthusiastic is Russia’s Vladimir Putin, an autocrat who invaded Ukraine, destabilized Europe, and backs Syrian regime bombs that are decimating civilians and hospitals in Aleppo.

Trump insists he could get a great deal from Putin (he describes almost every foreign policy move in terms of a deal) and, if not, he would walk away. What then? Declare bankruptcy in Ukraine and Syria and leave Eurasia to Putin? Does Trump have any idea who he is dealing with?

Or perhaps the deal that Trump wants with Moscow has less to do with foreign policy than business. As Bloomberg’s Josh Rogin recently detailed, Trump has been trying for years to expand his real estate empire to Russia. His new friend Putin may be just the contact he needs.

But back to foreign policy deals — does Trump have any clue about China (or trade deals for that matter) when he suggests that we can be friends with Beijing, while bending the Chinese to our will by imposing a 45 percent trade tariff. Is he serious?

There is a lazy ignorance to the presumptive GOP nominee that makes one wonder if he really believes his own mantras and thinks he doesn’t need to learn anything from books or experts. He certainly seems to have little appreciation of the world we live in, and has yet to surround himself with those who know better.

He clearly yearns for the stability of the Cold War, but those days are long gone, and foreign policy is far more complex in a very fragmented world.

As his speech made clear, Trump’s only foreign policy strategy is to stoke American fears and to posture about quick, painless solutions, while predicting that allies will pay up and enemies quail after he is elected.

When none of this happens, he has little to offer, appearing ready to withdraw into an isolationism that would endanger the country, or to strike out blindly.

The Trump foreign policy doctrine can be summed up in one word: meshugaas.

— Trudy Rubin is a columnist and editorial-board member for the Philadelphia Inquirer.