President Donald Trump isn’t happy with Germany — and the feeling is mutual. Last week, he tweeted that the United States has “a MASSIVE trade deficit with Germany, plus they pay FAR LESS than they should on NATO . . .”

Speaking at a rally, German Chancellor Angela Merkel replied in kind, saying, “The times in which we can fully count on others are somewhat over,” and putting the United States on a par with Russia as nations with which Germany needs good relations.

Trump isn’t entirely in the right in this clash. But he’s more right than wrong. His idea that trade surpluses are always good and trade deficits are always bad is wrong. In the end, trade is an exchange of goods among individuals. If our government attempts to make it harder for us to buy what we want from abroad, it’s trying to tell individual Americans what we should do with our own money. That’s wrong.

But there are legitimate criticisms to be made of German policy. For one, Germany seeks to run a trade surplus. That means it’s not importing enough from the rest of Europe.

And that makes it harder for nations like Greece to earn money to pay creditors, including German banks. So Germany’s pursuit of a trade surplus is self-impoverishing and destabilizing. Trump might bear that in mind.

But then there’s the question of NATO, and of U.S.-German relations. Trump is right about Germany’s military spending. The heart of the transatlantic security deal has been that the United States helps Europe, and Europe helps itself.

Yet Germany is only spending 1.2 percent of its income on its own defense. That’s miles below the NATO minimum of 2 percent, and the blame for that shortfall rests on Germany.

And Germany’s not in a strong position to complain about U.S. unreliability.

In 2003, Germany led the split in NATO against the United States over the Iraq War. Blame that stab in the back on George W. Bush, if you will. But Germany was just as unhelpful when it came to President Barack Obama’s intervention in Libya in 2011.

Germany likes to laud itself for the sanctions it imposed on Russia after Moscow’s invasion of Ukraine in 2014. But for a nation in Germany’s position at the heart of Europe, those sanctions were pathetically weak. Without U.S. pressure, they wouldn’t have happened at all.

And it was Merkel herself who, without consultation, gave the green light to millions of migrants from Syria, and elsewhere, to move to Europe. This will have consequences for Europe and the United States that can’t be measured.

Finally, the German people are reliably among the most anti-American in Europe — and that didn’t change under Obama, despite his leadership from behind. About 70 percent of the German public opposes a trade agreement with the United States.

Frankly, I’m tired of being lectured about being a good ally by Germany. If you want good allies, be a good ally yourself. Over the past 15 years, Germany has been a bad ally.

Despite this, I believe in NATO — because securing Europe is in American interests. We shouldn’t be deterred from doing right by ourselves just because we can’t count on a European member of NATO.

But that’s the problem. The more Germany’s unreliability becomes obvious, the more it encourages Americans to quit on NATO, and the harder it becomes for believers in NATO (like me) to make the case for it.

So when German leaders blame the United States for being a bad ally, they should look in the mirror: Those American concerns were born in Berlin.