NEW YORK • As if Western politics were not volatile enough, a wave of recent elections seems to offer contradictory evidence as to whether populism is advancing or receding.
It triumphed in the British vote to leave the European Union and in the US presidential race, fell short in the Dutch elections, and won its greatest ever success in France's first presidential round but faces likely humiliation in the second.
These results may not be as contradictory as they seem. Research suggests populism has been growing since the 1960s. Four major elections from the past year show how this dynamic can play out.
A GRADUAL GAIN, ONLY NOW OBVIOUS
Ms Marine Le Pen, the leader of the far-right National Front party in France, demonstrated in the presidential election's first round how far her movement has come. In the second round, if polls prove correct, she will show how far it remains from taking power.
In 1988, the party won 14 per cent. In 2002, it gained 17 per cent; in 2012, 18 per cent. This year, Ms Le Pen won 21 per cent.
This process has been so gradual as to have been barely noticed until now. It only feels sudden.
While elections are unpredictable, Ms Le Pen is projected to lose the second round by as much as 20 percentage points.
The pace of the rising populist wave is too slow to alone propel her into power. This is the nature of populism's awkward size - too small to reliably win national elections, but large enough to reframe politics as a debate between globalism and ethno-nationalism.
SYSTEM CAN MAKE THE DIFFERENCE
For much of last year's US presidential contest, it looked as if Mr Donald Trump would take a path similar to Ms Le Pen's - unprecedented victory in the Republican primary followed by humiliating defeat in the general election.
In competitive primary contests, Mr Trump's support hovered around 30 per cent. Polls showed he was unpopular among supporters of more mainstream candidates, as well as most Democrats.
This led many analysts to conclude that, nationally, Mr Trump's support had a ceiling of perhaps 40 per cent, on par with Ms Le Pen.
But there was one crucial difference: Decades of partisan polarisation within the two-party system in the United States.
While Mr Trump did win some working-class Democratic voters, his greatest leap came when once-sceptical Republicans rallied around him, pushing him past his supposed ceiling. And the Electoral College system meant Mr Trump could win even while losing the popular vote by 2 percentage points.
While France's centre-right parties feel comfortable rejecting Ms Le Pen, the Republican Party saw little choice but to back Mr Trump.
Polarisation, though less extreme elsewhere, is playing out across Western societies, driving once- centrist voters towards more extreme parties on the right and left - spaces often occupied by populists.
TOO LARGE TO IGNORE
Western establishments, after months of alarm, celebrated the Dutch elections in March as a sign that the populist tide had turned.
The far-right Party for Freedom, led by Mr Geert Wilders, grew to 20 seats from 15 to become the country's second-largest party.
In the end, it won only 13 per cent of the vote,not enough to force its way into a governing coalition. Dutch voters seemed to have ended the string of populist victories.
But Mr Wilders had been held back by the mathematical tyranny of parliamentary systems, not just by an anti-populist backlash.
In parliamentary systems, votes tend to be split across several parties, with none securing a majority on its own. To govern, parties have to form a majority coalition.
So as long as a populist party does not win over half of the vote - virtually impossible in systems like that of the Netherlands - the others can form a coalition excluding it, known as a "cordon sanitaire".
Yet even though Mr Wilders did not take control of government, his movement and policies advanced.
The centre-right party, which leads the government, held power partly by co-opting Mr Wilders' message, particularly on immigration. Prime Minister Mark Rutte told migrants shortly before the vote: "Act normal or leave."
Similar forces could play out in the French legislative elections in June. Even if Ms Le Pen loses, establishment parties have fractured and centre-right parties have grown more populist. Her centrist opponent, Mr Emmanuel Macron, will face pressure to move right as well.
As more populist parties become their country's second or third largest, mainstream parties will have to form more "cordons sanitaire" to keep them out. To populist voters, it feels like an establishment conspiracy to repress popular will.
Even if populist parties are often too small to take power, when the correct forces align, they are powerful enough to reshape politics.
This is how the UK Independence Party (Ukip) helped bring about the British exit from the EU. After years of single-digit shares in national elections, the party won 13 per cent of votes in 2015, again tracking with the measures of broader trends.
It had only one seat in Parliament, won by an MP who later quit the party. But that victory helped cause the centre-right Conservative Party to fear that it could lose power, or that its centrist leadership could fall, unless it co-opted Ukip's appeal. So it decided on a referendum on leaving the EU, seeming to believe the vote would fail. After all, 13 per cent was not much.
But Brexit passed with 52 per cent, because of support from voters whom the scholars Dr Jonathan Mellon and Professor Geoffrey Evans termed "Ukip curious" - those who were unwilling to consistently support the party but were receptive to its message.
"We live in an unprecedented era of volatile party support," the scholars wrote, meaning even a party as marginal as Ukip could put enough pressure on the system to force its policy onto the agenda. This hardly means Ukip will someday take power. But it hardly needs to. As Brexit proves, the populist wave can do plenty at 13 per cent.