As up to 400 million Europeans prepare to vote for the EU parliament, the populist challenge to the Brussels consensus has been disrupted by scandal.
In Austria, the far-right vice-chancellor has resigned in disgrace after falling victim to a hidden camera sting as he appeared to seek Russian backing.
Britain's Nigel Farage, the leader of the new Brexit Party, has led a strong campaign but has been dogged by questions about where his money comes from.
And in France, veteran far right-winger Marine Le Pen has been forced to deny that former Donald Trump adviser Steve Bannon has any role in her campaign.
The cloud of scandal partly overshadowed coverage of Italian hardliner Matteo Salvini's pre-election nationalist European unity rally in Milan on Saturday.
So far, there is no sign these wobbles will blunt the advance of populist forces in this week's polls, but they have opened space for centrist critics.
- 'Help slow the advance' -
German Chancellor Angela Merkel spurred the mainstream counter-attack at the weekend, urging EU voters to reject nationalist "politicians for sale".
Matthias Jung of German pollster Forschungsgruppe Wahlen told the Tagesspiegel that the scandal could help "slow the advance of the populists".
In Britain, meanwhile, the Electoral Commission announced Monday that it would review the online fundraising of Farage's fledgling Brexit Party.
And the man himself was hit by a milkshake thrown by a protester as he campaigned in northern England.
Nationalists, eurosceptics and the populist far-right are expected to improve their representation in the European Parliament in the election.
But it is not clear they can work together closely enough to disrupt the pro-EU consensus, even if the main centre-left and centre-right parties suffer.
Turnout has traditionally been low in the pan-continental vote, however, and mainstream politicians are hoping the scandals will mobilise the electorate.
In France, President Emmanuel Macron's liberal Renaissance movement is battling to win more seats than Le Pen's National Rally.
Macron's supporters denounced Bannon's presence in France, and accused the European far-right of serving as a "Trojan horse" for Trump and Russia's President Vladimir Putin.
In Austria, protests erupted after Vice-Chancellor Heinz-Christian Strache was caught on video offering favours to a woman purporting to be the niece of a Russian oligarch.
Chancellor Sebastian Kurz, who tried to tame the far-right FPOe by tying it into a coalition with his conservative People's Party, pulled the plug and called early elections.
The European Parliament, which will be elected in votes across 28 nations between Thursday and Sunday, has never been more important in framing the continent's laws.
But each vote since the first one in 1979 has seen a lower turnout than the last, and much of the energy in this year's race has come from those opposed to deeper integration.
- Main parties losing ground -
No big personalities have emerged among the candidates to lead the European Commission, the top job in Brussels and one that will be assigned by Europe's national leaders.
For now, only Britain is on the verge of quitting the bloc altogether, but eurosceptic and europhobic parties of various flavours are mounting a challenge.
Polling at the start of the campaign period pointed to around 173 members being elected from these groups in the 751-member Strasbourg and Brussels assembly.
And the main centre-right and centre-left groupings that have dominated pan-European politics in recent years look set to lose ground.
According to opinion polls, the top two groups could lose 30 seats each, meaning they will not be able to form a majority and may have to reach out to liberals and Greens.
The liberal ALDE hopes for an infusion of new blood from Macron's Renaissance and from the Spanish party Ciudanos.
For Brussels insiders, the big night will not be Sunday when the first results of the parliamentary race emerge, but two days later when the national leaders meet for dinner.