Prime Minister David Cameron makes his last campaign trip to Scotland on Monday. By the end of this week, he will know whether the country he was elected to run has shattered on his watch.
The polls suggest the Scots' decision whether to end the United Kingdom and go their own way is on a knife-edge. If they choose independence, it is hard to see how David Cameron could lead his party into the next general election in May 2015.
The "Rump UK" left behind without Scotland (no one even has a name for the remainder country yet) would probably end up over time with more Conservative governments as Scotland tends to elect Labour MPs to Westminster.
But the immediate thoughts of the Party of Winston Churchill and Margaret Thatcher would be dominated by a sense of humiliation and loss.
Even if the Scots choose to stay in the UK it looks like it would be by a narrow margin and political life will be convulsed in ways David Cameron neither predicted nor wanted.
So could David Cameron have dealt with all this differently?
Way back in 2011 when David Cameron first confronted the issue of whether he should allow a referendum (power over such constitutional matters still rests with the UK government) his advisers thought he could swat the independence cause with a hefty victory. Support for independence often didn't make it over the 30% mark in some polls.
While there was lethargy and a lack of buzz on the pro-union side, Alex Salmond's campaign team was creating a grassroots campaign that has elements of the Europe-wide anti-Iraq war campaign grafted on to the first Obama presidential campaign.
But did there have to be a referendum? Did there have to be a referendum quite like this one? But did there have to be a referendum? Did there have to be a referendum quite like this one?
The man who was Alex Salmond's policy chief until 2012, Alex Bell, says ministers at the top of David Cameron's coalition floated an offer of big new devolution powers to Alex Salmond's team in the months after May 2010. Back then, Alex Salmond's Scottish National Party didn't have a majority in the Scottish government so wasn't going to have the mandate to pressure London to demand a referendum. Big new powers, volunteered by London to Edinburgh, might have quelled the calls for independence, Alex Bell believes. But David Cameron didn't go down that route.
Once Alex Salmond's SNP had won a majority in the 2011 elections for the Scottish Parliament, David Cameron felt he had to allow them the referendum they wanted. But he could have signed up to a two option ballot paper which Alex Salmond was pushing for: offering the Scots voters independence or much more devolution ("Devo Max," as it became known). David Cameron turned that down too.
The team at 10 Downing Street (and the main Labour opposition party) were deeply suspicious of the Salmond wheeze and thought independence wouldn't appeal to enough people to be a worry. Well, it's worrying them now.
Having done down the route of a straight independence vote, senior figures in the UK government ignored advice from veterans of the Canadian government that fought and won Quebec's second referendum on independence in 1995. They said the UK government must have a clear, rival offer to independence. The UK government, along with the two other main parties in Westminster, only cobbled that together last week when the polls put independence support in the lead and when many Scots had already cast their postal votes.
In the meanwhile, a lot of Scots had come to see the debate as a binary choice between "independence" versus "no change." The "more powers" offer from David Cameron and the Labour and Lib Dem leaders may be what pulls Scotland back from independence at the last minute but it has come too late for many who've grown comfortable over time with the idea of independence, too late to avoid this heart attack moment for the Westminster establishment.
Even if he wins a narrow victory, a giant question mark will be placed next to David Cameron's judgement in the minds of many in his party. He will have to convince a restless Conservative Party that his hastily assembled plan to rush through devolution to Scotland is not unfair to England.
His plan to hold and win a referendum to keep the UK in the European Union looks a lot shakier given his stewardship of Scotland's referendum.
The referendum some in the Cameron team thought was a sideshow has turned into the main show. And main shows don't get much bigger or immediate than whether your country can survive the week.