Today's joint appearance by David Cameron and Nick Clegg is the latest attempt to shift the focus away from what divides the two parties (Lords reform and much else) and onto what unites them - in particular the urgent need for action on economic growth. A "mid-term review" is also promised.
While necessary for government stability, the continued closeness of Cameron and Clegg is far from being a sufficient condition for government effectiveness, at a time when large elements of the two parties resemble a coalition of the unwilling. On both sides, backbenchers and grassroots members are exercising growing pressure on the leadership to take a more assertive stance in dealings with their coalition partner and to prioritise distinctive party policies over shared coalition commitments.
Coalition governments around the world are familiar with this dilemma of how to balance government unity and party identity. In the UK case, the initial coalition agreement rightly ensured that both sides had something to cheer about in key areas - from immigration and welfare reform on the Conservative side to political reform and the pensions guarantee for the Lib Dems.
But come the next election, due in 2015, the two parties will be defending a joint record and, to a large extent, they will stand and fall together on this. The central priority for both parties must therefore be to make a success of the government and to deliver concrete improvements in areas of importance to voters - the economy, public services, taxation.
The negotiations of May 2010 achieved an impressive degree of consensus between the two sides, but five days of highly-pressured talks could never have set out a complete five-year strategy for the government. Effective coalition government therefore requires continuous negotiation and compromise as part of the ongoing policy-making process.
Ministers realise this, but do the wider parties? On both sides, there is a tendency to oppose new policy ideas on the grounds that they were "not in the coalition agreement". Tory rebels used this justification for their opposition to Lords reform - to which the programme for government committed only to "establish a committee to bring forward proposals". Michael Gove's draft proposals on abolishing GCSEs in their current form ran into a similar objection from the Lib Dems.
The danger is of lowest-common-denominator policy-making, where reform advances at the pace of the slowest (if at all) and little gets done in vital areas. A proper policy review could offer a way out of this difficulty, as the Institute for Government argued in A Game of Two Halves, our recent report on the coalition.
But the mid-term review must be more than a report card in which the government trumpets its achievements to date. Instead any review must be seen as an opportunity for reflection and learning about what has gone well so far, and what has not. Given the state of the economy and the public finances, the review also needs to be rigorous about prioritisation: what exactly is the coalition seeking to accomplish in its remaining time, and how will it go about doing this? To keep the restless backbenches on side, there will need to be some 'meat' for either side, but in many areas it will surely be necessary to admit that consensus is unattainable - with further policy development shifted to the separate manifesto processes.
After the early unity of the 'rose garden phase', the coalition has been increasingly relaxed about "differentiation" between the two sides. But there are two competing conceptions of what this should mean. For the pro-coalition wings of both parties - as a senior government adviser told us - differentiation should mean "more open debate, which is a good thing for democracy and for government" but with the two sides ultimately seeking compromise and moving forward together. But for coalition-sceptics on both sides (of whom there are many), differentiation is seen as more akin to trench warfare than diplomatic negotiation. To this mindset, blocking the enemy policy is a key objective, even if ones own priorities similarly perish in no man's land as a result.
The future of the coalition depends on the struggle between these two perspectives within both of the coalition parties.