Carl Bildt is a former prime minister of Sweden and a contributing columnist for The Post.

Observers in Europe are following America’s election campaigns with disbelief, a good portion of dismay and distinctly growing apprehension.

Campaigns are, of course, campaigns, and any seasoned politician or observer of politics knows that the relationship between the words of campaign and the deeds of office isn’t always straight.

That explains the muted reactions to Hillary Clinton’s oscillations on trade policy. But it’s starting to creep in that she might have boxed herself in on the issues to such an extent that a retreat will hardly be possible.

The global economy is not in stellar shape, global trade growth is sluggish and there is a silent war over whether the West or China will set the rules for the games to come. Much will depend on whether the Obama administration will manage to get the Trans-Pacific Partnership trade deal ratified, but if this fails and we are confronted with either a hesitant Clinton or a Donald Trump hostile to trade agreements, things could easily start to go wrong.

But for all the questions on Clinton’s vacillations on trade, the policies of a possible Trump administration spark something bordering on outright fear.

Some American friends tend to say that the United States is a country with strong institutions, constitutional separation of powers and clear limits on what a president can actually do.

Yes, but primarily on domestic issues.

Foreign-policy issues are a different matter. A stalwart Republican friend of mine, with vast experience on foreign policy and security issues, said, “I know the power of the Oval Office, and that man must never ever be allowed in there.” Whoever sits in the Oval Office is the commander in chief of the world’s mightiest military arsenal and can single-handedly take the country’s foreign policy in very different directions.

It’s fair to say that my friend’s feelings are widely shared across the world. Well, at least throughout the democratic West.

Some are starting, with reluctance, to consider what a Trump administration might actually mean. If disaster strikes, what are we supposed to expect on Jan. 20?

Trump’s trade policies are certainly scary, but apprehensions concerning these pale in comparison to the potential geopolitical consequences of him entering the Oval Office.

Trump has evidently already looked into the soul of Vladimir Putin and concluded that he is a strong leader and a good man, and that anyhow all this talk about democracy and respecting rules isn’t anything for real men of their caliber.

A good guess is that as president, he will try to achieve some super-Yalta deal with the Kremlin, saying that “Make Russia Great Again” is an honorable goal, concluding that might is better than right and agreeing that the quarreling Europeans in Brussels, or wherever, need not be taken too much into account.

Whatever the content of such an approach, Trump risks creating a new instability in Europe. And with the United Kingdom going into a frenzy on what to do after the Brexit vote, we are already in a somewhat fragile situation. Without a common framework, the risk is that different countries will go in different directions, leaving an opportunity for the Kremlin to seize, make its moves and destabilize Europe even more.

What will happen then is anyone’s guess. Trump in the Oval Office might swing from appeasement to aggressiveness in seconds, or he might just walk away from it all, leaving the Kremlin to start to pick up pieces here and there. Either way, it would be very dangerous.

And then there is, of course, the Middle East.

Here the risk is obvious: Trump will provide a powerful boost to a Daesh that at the moment is starting to come under pressure — from its own failings more than from the efforts of others. But moving the U.S. Embassy from Tel Aviv to Jerusalem would move sentiments among disenchanted Arab youth in the direction of militancy in a way hardly any other step could.

Few strategic mistakes would be as profoundly grave as stoking a war between Islam and the West. But Trump’s own words indicates that this is what he, by design or by default, would actually do. While Trump can try building his walls around the United States, Europe is in a different situation. Beyond geographic proximity to the Middle East, Islam forms a part of our societies; any profound confrontation along these lines risks having profound effects across large parts of Europe.

The uncomfortable fact is that in the Middle East, a gradual but determined effort to overcome divisions, heal wounds, reform economies and build functioning and legitimate states throughout the region is the only possible way forward to avoid a combined Daesh/al-Qaeda 2.0 challenging us a decade from now.

A Trump presidency risks smashing any such strategy into smithereens.

No responsible European politician is coming out in public taking sides in the United States’ political affairs. That’s the way it should be between nations — we respect each other’s democratic choices. But in the chancelleries of the democracies of Europe, there is no doubt whatsoever what they fear.

Europe is already confronted with the revisionism in the East and the implosions and explosions in the South — but now there is a lingering feeling that the most dangerous developments could actually come from the West.