Forget sweeping spending cuts, the AV referendum row and divisions over Europe. The biggest risk to the coalition could come from a self-inflicted wound.
Shaking up Britain's electoral map was a Tory idea. It was the price they demanded, this time last year, for allowing their junior coalition partners, the Liberal Democrats, a referendum on the alternative vote.
Twelve months later, and the Lib Dems have lost the referendum. They are as unpopular as ever. But the legislation has been passed. The Conservatives are left laughing. For the number of MPs will fall from 650 to 600 in 2015, helping their cause.
At least, it's supposed to. The Commons must approve the changes which will eventually be put forward by the Boundary Commission in full by October 2013 at the latest. This is the key vote which, a Tory party elections analyst has said, is the greatest single risk to the coalition making it through its full five years.
Imagine you're a Tory MP - perhaps used to being returned with a comfortably-sized majority election after election. All of a sudden, you receive a phone call from someone at CCHQ. They're terribly sorry, they explain, but due to boundary changes your constituency is about to disappear off the face of the Earth. But you were going to retire anyway, weren't you?
Perhaps you're one of the many, many new MPs who only got into parliament because so many of the expenses-shamed old lot retired last time around. You're told that your seat, which you only just managed to win last time, has just taken in three weighty wards packed with Labour voters. The odds are now heavily stacked against you. But you'll fight the good fight, won't you, dear chap?
Worse still, imagine being a Lib Dem junior minister. Unexpectedly promoted to government as part of the coalition. Forced to make uncontroversial comments of acquiescence as the Tories rapaciously tear down the welfare state, the NHS and any other public service they can get their right-wing mitts on.
And then, thanks to boundary changes demanded by Nick Clegg as the price for a failed referendum, you find the goalposts are shifted. Your tiny bit of orange on the electoral map is about to be engulfed by voters from neighbouring Tory or Labour seats. The opinion polls are bad enough, but now this, too?
These won't be fictional scenarios in just a couple of years' time. Such is the extent of the boundary changes - only around 25 seats at most will emerge unscathed - that MPs on all sides are going to find themselves in unexpectedly tough situations.
In some areas, two MPs from the same party are going to find themselves playing musical chairs - with room on the constituency map for just one of them to remain in parliament. In others, the local party might decide they'd rather have a new candidate in place after all, given that the changes are as extreme as they are. As one backbencher told me: who's going to employ a 48-year-old former MP?
As the general election approaches there will be a natural drift towards open warfare between the two parties in government. The sweetness of the Cameron-Clegg honeymoon will be but a distant memory. And with impeccable timing - just as the Tories and the Lib Dems drift towards an election footing - the Commons will be asked to approve the boundary changes.
Will all those turkeys really vote for Christmas? Many opposition MPs doubt it. If the Commons vote fails the 2015 election will be run on the old boundaries, after all. Wouldn't that be a preferable outcome for all those fed-up coalition MPs who've been let down by their party?
It's certainly a possibility. Much will depend on whether, between now and then, the parties can settle these 650 separate headaches amicably. Insiders secretly acknowledge an awkward, tantalising truth: they won't be able to please everybody. If the rebels get their way, it may be time for an election sooner than we'd thought.