British voters face a momentous choice tonight, when they'll vote on whether to remain in the European Union.
A decision to leave might badly hurt the economy, which relies on Europe for trade and investment - but the repercussions would go wider than that.
The larger European project would also be in danger. An enterprise that secured peace on the continent after World War II, moved hundreds of millions of people toward greater prosperity, and helped entrench liberal democracy in Eastern Europe after the Soviet collapse would be gravely damaged.
The risks are huge - yet recent polls show the Leave campaign is leading. Europe's governments are waking up to the fact that "Brexit" might actually happen.
Britain faces an unsolvable dilemma. Its economic interests tell it to stay, especially since the UK has negotiated an advantageous status within the union: full access to Europe's integrated markets, but without the single European currency, which has proved so detrimental to the economies of many other EU members.
Yet Britain won't ever be comfortable with the EU's larger political ambition to create an "ever closer union".
If they choose to stay, Brits will resent the steady erosion of their power of self-government, which voters see as the hollowing out of their democracy.
Whatever Britain decides, it's sure to regret it.