Barack Obama comes to London next week to tell Britain to stay in the European Union if it knows what’s good for it.

British Prime Minister David Cameron waves as he leaves a European Union leaders' summit in Brussels February 20, 2016. Cameron said on Friday he would campaign with all his "heart and soul" for Britain to stay in the European Union. REUTERS/Yves Herman

The U.S. president is something of a puzzle for the Brits. He told Jeffrey Goldberg of The Atlantic that Prime Minister David Cameron screwed up on Libya, producing the current state of radical instability there, because he was “distracted by a range of other things.” He warned Cameron that he better spend more on defense if the special relationship between the two countries was to last. (Britain’s expenditure is rising again to its previous level, and the NATO minimum, 2 percent of GDP, for the next five years.)

Yet, on his first presidential visit to the United Kingdom in 2011, where he was accorded the privilege of addressing an audience in the Westminster Hall, core of England’s ancient parliament, Obama gave a speech of such warmth that he brought tears to the eyes of the members of Parliament present. “I’ve come here today to reaffirm one of the oldest, one of the strongest alliances the world has ever known… our relationship is special because of the values and beliefs that have united our people through the ages.”

Of course, any close friendship has its quarrels. I believe Obama was right to criticize the UK, and other EU states, for doing too little to stabilize post-Gaddafi Libya -- so determined are the present European governments to avoid the morass of post-Saddam Hussein Iraq. But the warning he will deliver on the EU will -- if ignored -- mean a real loosening of transatlantic bonds, as would a British vote to leave the EU, on June 23. No president (it will soon not be Obama) can value a relationship intent on self-harming.

U.S. trade representative Michael Froman has said, in an understated sort of way, that “we are not particularly in the market for free-trade agreements with individual countries,” when asked about prospects of a U.S.-UK deal. As Edward Luce wrote in the Financial Times, that means “A special trade deal with the United States? No chance.”

Still, the outgoing Mayor of London Boris Johnson, who is staking his bid for leadership of the Conservative Party on enthusing the campaign for Britain’s exit, branded Obama’s call for the UK to remain in “a piece of outrageous and exorbitant hypocrisy.” He has a point. As he said, “there is no country in the world that defends its own sovereignty with such hysterical vigilance as the United States of America.”

The United States refuses to be a member of several international agreements -- the jurisdiction of the International Criminal Court, the Convention on the Law of the Sea -- in the name of national sovereignty. It would no more think of transforming the North American Free Trade Agreement into an “American Union” with a supranational executive than apply to become a British colony once more. (Nor, I guess, would Canada, nor Mexico.)

Yet it does so, in significant part, because it is the leader of the free world. Even if Obama has sought to push other states to step up to the plate of sharing the sheriff’s job more actively (the context in which he criticized Cameron over Libya), he cannot escape the position, and the special status he must maintain because of it. And since he does occupy that position, it’s incumbent on him to warn that were the UK to leave the EU, it would suffer, and the EU and thus the Western world might suffer more.

Three large issues stand between the UK and continued membership of Europe. One, the most obvious, is the disarray of the EU itself, no great advertisement for a renewal of Britain’s dues. A renewed economic crisis could beset Greece, as its economy stubbornly refuses to recover. The immigrant flow from Turkey to Greece is partly staunched, but the deal with Turkey to take back those refused entry is in danger of collapsing, and better weather will mean renewed crossings from North Africa to Italy. Immigration is at the top of British worries about the EU, and there’s little to suggest that concern will be calmed soon.

Less obvious is the UK’s own international/national struggles. Scotland is likely to re-elect the Scottish National Party as the regional government in elections early next month: polls show the SNP could increase its comfortable majority, and again seek assent to independence. Northern Ireland’s peace agreement, negotiated nearly two decades ago, which ended most IRA terrorism by giving its political wing, Sinn Fein, a part in government, is permanently shaky. England, which accounts for 90 percent of the British population, finds its own, buried nationalism increasingly attractive. These internal convulsions have rendered a country once a byword for stability into one seeking a refoundation of its national sense of itself. Europe is almost a distraction.

And the sense of élan that the EU had -- that it was the future -- has almost entirely gone. To read the speeches of the Union’s founders -- as the French Foreign Minister Robert Schuman, the German Chancellor Konrad Adenauer, the Italian antifascist Altiero Spinelli -- is to enter minds with one dominant thought: to create a federal state whose component parts could no longer go to war. Schuman, whose proposal for a European Coal and Steel Community was the basis of the Union, said in 1950 that it “will lead to the realization of the first concrete foundation of a European federation indispensable to the preservation of peace.” “In my opinion,” wrote Adenauer in his memoirs, “the European nation states had a past but no future.” Little of that remains and no strong ideal has taken its place.

Obama would be advised not to tell the British that Europe is their destiny, their political future. Best to say: if you leave, you will damage a fragile world order; you will do yourself a grave disservice. It’s a speech which should be summed up in a phrase: not good, but could be worse. And hope the practical British get the point.