EU referendum: Time to focus on the real question
The prime minister, who once urged his party to stop banging on about Europe, has willingly chosen to be remembered for doing precisely that.
Over the next four months David Cameron will campaign, he promises, with all his heart and soul, to secure our place in the European Union.
He has the support of most of his cabinet, most of the political establishment, Labour, SNP and Lib Dem MPs.
Yet many of his colleagues will oppose him loudly and proudly.
The demand for a referendum went from the margins to the mainstream of the Conservatives in part because of the rise of UKIP, but also the chaos of the eurozone crisis and its seeming inability to deal with its profound problems. Now - in or out, is politics' central question.
And despite the polite promises of civilised debate, Mr Cameron is risking the unity of his party with the vote.
Cabinet ministers, finally allowed to speak out today like Iain Duncan Smith, and Michael Gove rushed straight from Downing Street to work the phones for one of the leave campaigns.
The gang of six who posed awkwardly for photographs could well become seven when Boris Johnson breaks his continuing silence.
But whatever the individual calculations, expressions of opinion on either side, are dwarfed by what today's announcement finally confirms.
That in 123 days British voters have the chance to choose to step away from one of the institutions that has shaped our laws, and all of our lives, for more than 40 years.