Why is the Middle East in flames and Russia on the rampage? In both Europe and the Middle East, it is common to hear the blame placed on Mr Barack Obama. The United States President, it is charged, is a weak and disengaged leader who has allowed international events to get out of control. Many Americans - both liberals and conservatives - make the same accusation. Mrs Sarah Palin, darling of the American right, has called Mr Obama "capitulator-in-chief". Mr Roger Cohen, a New York Times columnist, has blamed Syria's agony on the "fecklessness and purposelessness" of the Obama administration.
Those who yearn for a more muscular US foreign policy often assume that Mr Obama will prove to be an aberration - and that the next president will "put America back in the game". But that could well be a misreading of the underlying direction of US politics and foreign policy. The current front runners in the presidential election campaign - Mr Donald Trump on the Republican side and Mr Bernie Sanders for the Democrats - have embraced ideas that are isolationist, in all but name. If those ideas prevail, they would make Mr Obama look like a super-engaged internationalist.
Even if Mr Trump and Mr Sanders never get close to the White House, the popularity of their campaigns - and their influence on the more mainstream candidates - suggests that there is now a strong constituency in the US for a retreat from globalism: Repudiating international military and economic commitments.
The inherent isolationism in Mr Trump's thinking can be disguised by his chest-thumping rhetoric about rebuilding the military and getting tough with foreigners. But it is no accident that his signature initiative is to build a gigantic wall along America's southern border. Mr Trump's economic rhetoric is all about shutting out the world. He is the most explicitly protectionist candidate in the field, promising, for example, to make sure that Americans buy US-made cars and machinery, not Japanese imports. He denounces the trade deals that the US has signed as bad for the country and has pledged to rip them up.
He takes a similarly mercantilist attitude to security, promising to force South Korea and Japan to pay for America's military protection. The implication is that there is no inherent US national interest in underwriting the security of the Asia-Pacific region. That logic, taken to its obvious conclusion, would be a formula for America pulling back from its security commitments all over the world.
Mr Trump is also a frank admirer of Russian President Vladimir Putin, calling him a "strong leader" and basking in Mr Putin's praise. In a recent Republican debate, all the presidential candidates queued up to denounce Mr Obama for not crushing the extremists of the Islamic State in Iraq and Syria, but none mentioned Russia's intervention in Syria. As a foreign policy "realist" and self-proclaimed deal-maker, Mr Trump would undoubtedly be attracted to granting Mr Putin his longed-for Russian "sphere of influence" in Eastern Europe. And once that is done, why not cut a similar deal in East Asia with Chinese President Xi Jinping, another tough-guy foreign leader who Mr Trump openly admires?
Mr Sanders has not embraced the militarism of Mr Trump's view of the world. Instead, he has opted for the left-wing version of isolationism: Denouncing the idea that America should be "policeman of the world". Mr Sanders also has a Trump-like distaste for free trade, proclaiming: "Unfettered free trade has been a disaster for working Americans."
Together, Mr Trump and Mr Sanders are capitalising on growing American disillusionment with globalisation. The living standards of middle-income Americans have been under pressure for decades, and foreigners and an internationally connected elite are easy scapegoats. Both the far right and the hard left in America are now promising a retreat from globalisation. But any such retreat would have profound consequences, not just for the international economy, but for America's role as the world's most powerful nation.
Of course, both Mr Sanders and Mr Trump are still a long way from the White House. The bookmakers' favourite to be the next president remains Mrs Hillary Clinton. And yet, even she has had to respond to the new public mood. Last week, she adopted Mr Sanders' claim that the economy is "rigged" in favour of a privileged elite.
Those who yearn for a more muscular US foreign policy often assume that Mr Obama will prove to be an aberration - and that the next president will "put America back in the game". But that could well be a misreading of the underlying direction of US politics and foreign policy.
Mrs Clinton has also come out against the Trans-Pacific Partnership (TPP), a new trade deal that she once championed as secretary of state. As president, Mrs Clinton would probably find a way of supporting the TPP, which she used to argue is a crucial part of America's "pivot" to Asia. She certainly takes a conventional "establishment" view of the importance of American leadership in the world.
But the current course of the presidential election suggests that it would be foolhardy to dismiss the chances of either Mr Trump or Mr Sanders actually winning their parties' nominations and, ultimately, the presidency.
If that were to happen, the commentators bemoaning the "weakness" and "fecklessness" of Mr Obama would come to realise that, in fact, he might be the last in a line of serious and committed internationalists to occupy the Oval Office.
THE FINANCIAL TIMES