"Things fall apart; the center cannot hold; Mere anarchy is loosed upon the world."
It's time to quote W. B. Yeats' famous poem again. But this time, it really does seem that the political center is under intense pressure — from left and right — all over the Western world.
In Britain, David Cameron's center-right government faces a revolt over his country's membership in the European Union. In Germany, Angela Merkel's broad left-right coalition is being battered for her handling of migration.
Across Europe, governments that occupy the center ground find themselves struggling against energized ideological movements from right and left.
In the United States as well, the centrists are under siege. Hillary Clinton faces the most serious left-wing challenge to a mainstream Democrat in decades. On the Republican side, the moderates have mostly collapsed.
The party's establishment is now coalescing around Marco Rubio, who, when elected, was described as "the first senator from the tea party."
The populists and radicals have filled space that the major parties vacated.
After the end of the Cold War, political parties in the West started moving to the center —among others, Britain's Labour Party, the Italian and French socialist parties, and America's Democrats. (Geoffrey Wheatcroft writes of the phenomenon in Europe in The National Interest.)
The Republican Party is a partial exception to this rule. Yet even there, the last two GOP presidents — the Bushes — governed from the center, certainly enough so to enrage their conservative supporters and fuel insurgencies. (George W. Bush's problems related more to competence than ideology. He did enact a ruinous tax cut, but other than that was a big spender, supported education standards, and expanded Medicare.)
Why are centrists so vulnerable?
The reality is that these moderate politicians have actually performed well in recent decades. Look at the challenges they faced — the end of the Cold War, the integration of Eastern Europe, wars in the Balkans, the rise of economic competitors, the Asian economic crisis, 9/11, the global financial crisis.
Western governments have managed to steer their countries through these difficult times with skill, maintaining peace, growing economies, and adapting to a new technological age.
The problem is that while they may be competent, centrists are dull, practical types. And there is always a search for romance in politics. Even amid centrist success, there are still enough problems to galvanize the romantics who believe the answer is a revolution.
For Bernie Sanders, it is a revolution from the left; for Ted Cruz, it is one from the right; and Donald Trump almost magically mixes and matches the furies of both ends of the spectrum.
David Miliband, the former British foreign secretary, remains the most effective spokesman for Europe's modern center-left. He argues that the left- and right-wing revolts stem from the same force — globalization.
"The right has no good answer to the problem that globalization erodes people's identities. The left has no good answer to the problem that it exacerbates inequality," he told me.
That leaves traditional politicians struggling to hold on to their supporters while outsiders promise easy answers. "The best lack all conviction," Yeats wrote, "while the worst are full of passionate intensity."
The simple solutions are, of course, non-solutions. And they mostly won't happen. We will not build a wall, nor deport 11 million people, nor place a ban on all Muslims entering America. Britain will not leave the European Union. (Even if it voted to leave, this would only begin a complicated new negotiation with the EU that would result in a new arrangement, much as has happened with the Danes and the Irish.)
And the EU will not crumble because a few countries put up borders to stop migrants and refugees from entering their lands.
But what is happening is political paralysis. The radicals and romantics might not have the power to overturn the centrist consensus, but they can place it under relentless pressure.
Cameron will spend the next months consumed with opposing the forces of the so-called "Brexit." In the United States, the country and its political leaders have now spent months debating fantasies.
Meanwhile, there is no discussion of the important issues and the actual, plausible policy options to deal with them — regarding the global economic slowdown, massive infrastructure deficits, growing inequality, and climate change, among others.
Yeats was wrong. The center can and does hold, but just barely.
Fareed Zakaria hosts CNN's "Fareed Zakaria GPS," and makes regular appearances on shows such as ABC's "This Week" and NBC's "Meet The Press." He has been an editor at large Time magazine since 2010, and spent 10 years overseeing Newsweek's foreign editions. He is a Washington Post (and internationally syndicated) columnist. He is author of: "The Post-American World." For more of Fareed Zakaria's reports, Go Here Now.