For both leaders, this must seem to be an expedient outcome. Amongst the more thoughtful sections of the politically-engaged it is also supporting the abstract notion that Coalition government is in some way an end in itself. There is no obvious alternative configuration that would command a Commons majority, and there remains economic crisis and stagnation to address. Add to this the promotion of an "enemy within" mentality and there are strong reasons to support the continuation of the current arrangement, even as it saps the Liberal Democrats and masks the unpleasant rightward drift of the Tories.
Yet, the counter-factual seems to be missing. With two years to go, and the swivel-eyed backbenches doing their best to scupper any legislation not burnished in the forge of Farage-appeasement, the prospect of meaningful progress on any area of policy diminishes. Pre-election posturing has already begun, not least from the right-wing fellow-travellers whose unarticulated desire is to morph into UKIP-lite - creating a reactionary rainbow coalition inclusive of the street thugs of the EDL through to their uneducated, unthinking Eurosceptic brethren within the Tories.
The electoral landscape of 2010 provided very few options, and these have closed down further. It is getting very difficult to see what benefits the Liberals are securing from participation beyond a masochistic pleasure at being Cameron's human shield against the loons. As the minority partner, most of the distinctive, liberal policies that were in their 2010 manifesto have been lost - unless there is a political expedient (e.g. the cancellation of Labour's identity cards on cost grounds) - and it is difficult to envisage a remarkably-different economic strategy having emanated from Labour.
Yet this is not the whole story. While the Liberals have been compromised and outmanoeuvred, they have managed to restrain the lunatic section of the Tories - even to the extent where some Tory Ministers have had to remind their own constituency that the electorate may have despised Labour but they did not endorse any of the other parties to manage on their own. This creates a political space for the Liberal Democrats before the election - and the choice for them is whether or not they do this from within the Coalition or without.
The restraint on unfettered neo-con, authoritarian dribbling has been vital (and the benefit of Coalition government needs to be argued accordingly) but it needs to be made much more explicit. The refusal to emasculate and privatise the NHS, the refusal to engage in a demagogic race-to-the-bottom xenophobia surrounding our European partners, and the resistance to the further promotion of the banking parasite above the working human are all useful negatives to put alongside the start of a progressive reform of tax policy and at least some efforts to target spending where people need it most in education.
For Clegg, or, should he refuse to engage, his party, there is a choice ahead. Staying in power provides further dampening, but also the risk of more guilt by association. Sitting outside a Tory minority administration would allow them to promote extremist policies to test with the electorate - the Stupid Party has always flirted with this - while ensuring that there is no Commons majority to enact any such deranged wibblings. The left needs to think about how it pushes the Tories and UKIP into competing for the same space - creating space for reclaiming the more engaged Conservatives and setting out a democratic, socialist space.
The correct way forward is imponderable, but the collaborative, inclusionist phase of the Clegg-Cameron relationship is at an end. Both are wounded, marginalised and increasingly irrelevant to the post-2015 landscape. The Liberals, damaged possibly beyond repair, need to determine whether they are able to stand independently or being incorporated - and to do this in the context of possible deal-making with Labour. The choice will not be easy, but the need for a leftward shift becomes more evident by the week.