No-one can predict European politics
It has been a constant theme of European politics over the last few years.
In several countries we are witnessing a gradual decline in support for traditional mainstream parties, as disillusioned voters strike out in unexpected directions.
This loosening of old loyalties has been most notable in Greece: hardly surprising, in a country that has just lived through the steepest recession a modern industrial democracy has ever seen.
The radical left coalition, Syriza, is now in government.
The extreme right party, Golden Dawn - dismissed by its critics as a Neo-Nazi organisation - has a substantial parliamentary presence.
But is Greece a one-off? Or is it the canary in the coal-mine?
At first sight, elections in Spain and France this week suggest that the break-up of the centre-right/centre-left duopoly may not be quite as sudden as some expect.
But look a little closer and some of the numbers are still fairly remarkable.
In southern Spain the Socialist party won a closely-watched regional election in Andalucia, where it has governed since the restoration of Spanish democracy in the 1980s.
But Podemos from the radical left - the Spanish Syriza - won an impressive 15% of the vote; little more than a year after the party was formed.
The big loser in Andalucia was the centre right People's Party, which runs the government in Madrid, even though it came second overall.
The PP will be particularly concerned because the threat to the status quo doesn't come only from the left.
An upstart centrist party, Ciudadanos, also won 9% of the vote, attracting support from people disillusioned by business as usual.
So where does this leave the two main parties in Spain?
As recently as 2008, the Socialists and the PP between them won nearly 84% of the vote in a general election.
They won't come anywhere near that when the country goes to the polls later this year.
Podemos is still some way behind them. But it is indisputably on the rise.
More than a protest
In the first round of local elections in France this week Marine Le Pen's Front National did not top the polls, as many people thought it might.
But the FN still came second with more than 25% of the vote, pushing the governing Socialists into third place.
That suggests that support for the FN's anti-immigration, anti-EU message is more than a simple protest vote.
Even if the mainstream parties conspire to keep the FN out wherever they can in the second round of voting, the French elections are another sign that many disgruntled citizens are now ready and willing to look for alternatives.
Elsewhere on the continent there are similar stories.
The rise of the Five Star Movement in Italy or UKIP in the UK, or even the AfD (Alternative for Germany) in Germany, suggest that some political fault lines are moving.
Why is this happening?
The obvious answer is that it is partly the result of years of economic crisis, particularly in southern Europe.
For many voters, mainstream parties have failed to step up to the challenge.
But there's also a more general malaise - a feeling that ordinary lives are being buffeted by forces and institutions beyond the control of voters.
The idea of a 'democratic deficit' has exercised many political minds, particularly among supporters of the European Union.
Parties like Syriza and Podemos want to redefine what the EU does.
But many protest parties want to destroy it.
Of course, the centre ground is not dead.
Well-funded party machines do not disappear overnight (even if supporters of the Greek Socialist party PASOK may beg to differ).
But traditional parties across Europe are under pressure as never before in recent memory.
And European politics has become fascinatingly unpredictable.