Put another way, it will tell British lawmakers who is angriest.

There’s plenty of anger to go around: Those who voted in 2016 for Britain to leave the EU—52 percent—are frustrated that the goal has yet to be realized. Those who voted to remain—48 percent—are angry that Brexit could still happen at all.

If it sounds like this contest is shaping up to be all about Brexit, that’s because it is. Though European elections are ostensibly about electing lawmakers who will shape the EU’s future, they almost always end up being domestic affairs—and no subject is more dominant in British national politics now than Brexit. Paradoxically, the country that is debating the EU most intensely is the country that is set to leave.

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The temptation to treat the European elections as a proxy for a second referendum on Britain’s EU membership has already been seized by virtually every party in contention, and the idea appears to be spreading among voters too. A recent survey by the British polling firm YouGov projects that the nascent Brexit Party, which advocates Britain leaving the EU without a deal, could win as much as 35 percent of the vote—higher than the Conservative (9 percent) and Labour (15 percent) Parties combined. The anti-Brexit parties, which include the Liberal Democrats (16 percent), the Greens (10 percent), and the newly established pro-second-referendum party Change U.K. (5 percent), are projected to win a combined 31 percent of the vote.

Most European Parliament candidates I spoke with said that this election was being treated like another Brexit vote, but not all of them think it should be. “It’s a false promise that people will be selling, because we’ve already had a referendum—we’ve already had a decision,” Emma McClarkin, an incumbent Conservative MEP and Brexit supporter who represents England’s East Midlands, told me.

It’s true that victories for the Brexit Party and Change U.K. in the European elections won’t shift the makeup of Britain’s Parliament. For these new parties, though, that hardly seems to matter. To hear them tell it, the point of contesting the European elections is “to build a platform for a general election,” Alexandra Phillips, a Brexit Party MEP candidate for England’s Southeast region, told me. She said a Brexit Party victory in the European election would “send a very clear message back to the political parties in the U.K. about what it is they need to do”: deliver Brexit.

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Indeed, neither the Brexit Party nor Change U.K. appears to have any policies apart from Brexit. But both see the European elections as a springboard into national politics. “If we get any seats [in the European Parliament], it will be a triumph,” Gavin Esler, a Change U.K. candidate for London, told me.