It was at times like these that the Liberal Democrats used to come in handy. They were the political gaffer tape of David Cameron’s first term – never a permanent solution to anything, but a versatile way of holding together things that seemed otherwise certain to splay apart. Surprisingly durable too, until they came unstuck.

When Tory MPs were cross with Cameron for failing to do their bidding, the prime minister would blame Nick Clegg. He claimed to keep a “little black book” of policies sacrificed for the sake of coalition but ripe for rehabilitation. Help me win a majority, he told the restive troops, and you will see my true blue colours unfurl.

So how is that working out? Unshackled from coalition, Cameron and George Osborne are now at liberty to find extra billions of budget savings from the benefits bill. Except in so doing, they managed to provoke conscientious rebellion on the Tory benches over tax credits, and drive Iain Duncan Smith into self-certified compassionate exile from the cabinet.

Spared the impediment of Cleggery, Downing Street can roll out the next phase of health service modernisation, starting with a “truly seven-day NHS” as advertised in the Conservative manifesto. Except that it has blundered into a war of attrition with junior doctors over weekend working that will burn through any reserves of public confidence in Tory handling of health matters long before it yields a dividend in more flexible surgery hours.

With the tedious tag-along party expelled from Whitehall, the government can finish its schools revolution, compelling stragglers and naysayers who still lurk under local authority governance to embrace their brave new future in chains of academies. Except the rank and file are not alight with revolutionary fervour. Conservative councillors and MPs are in revolt; whips say a bill that enforces non-voluntary academisation would be mauled in parliament. Nicky Morgan insists the plan will go ahead, but in the emollient tones of a minister in tactical retreat.

Oh, for a division of Lib Dems! They could be relied on to march through the aye lobby, given a concession or two

On every front where Cameron once imagined advance towards a legacy of domestic reform – refashioning the state so it matches the challenges and fiscal constraints of the times – he is bogged down. The message is garbled, the purpose obscure, the legislative path blocked. Oh, for a division of disciplined Lib Dems! They could be relied on to march through the aye lobby, given a policy concession or two, a social mobility taskforce, a ride in a ministerial car, a bunch of grapes.

Senior Tories believe that parts of their manifesto were written to be dispensable in negotiations to renew coalition. Some also predicted that a slender majority would poison the chalice of victory, transferring parliamentary leverage over Cameron from biddable liberals to irreconcilable Eurosceptics; from newbie ministers, desperate to look responsible in government, to professional rebels.

That doesn’t mean a Lib Dem presence in government would have averted the present shambles. Labour always depicted Clegg’s role as something between a hostage and an accomplice. Lib Dems led cheers for Osborne’s benefit-stripping budgets, mangled but did not thwart Andrew Lansley’s health bill, tweaked but did not scupper Michael Gove’s education reforms. The riposte is that deeper, crueller cuts were averted, that greater licence for private-sector profiteering from public services was vetoed, that good deeds were done in the shadow of austerity in areas such as nursery care and infrastructure spending. Besides, the proof of a Lib Dem moderating influence is conveyed in the pungency of undiluted Conservative rule.

The audit of minor Cleggite achievements is pretty niche politics these days. The Lib Dems were handed no gratitude by voters last May, and precious little is in the post now. One way to see that fate is as a just penalty for collaboration with the wicked Tories. That judgment flows from a presumption that Cameron, Osborne, Hunt, Morgan and the rest are hellbent on destruction of the public realm because they are ideologically hostile to the idea of properly funded, state-run services. Their so-called reforms are presented as asset-stripping, with a barely hidden agenda of handing schools and hospitals over to corporate interests. That radicalised account of Tory motives, broadly endorsed by the Labour leadership, has helped ramp up the junior doctors’ dispute from a generic haggle over pay and conditions into a beacon of wider resistance against the government.

The radicalisation is reciprocal. Ministers become blind to reasonable grievance among public sector workers. They see trade unions as reactionary guardians of a mediocre and financially unsustainable status quo, at best. At worst they are presumed to be hotbeds of saboteur militancy, incapable of constructive dialogue. Each side serves up rhetorical excesses that can be seized upon by the other side to prolong a cycle of intransigence.

There is no happy outcome from polarisation of this kind. It guarantees that the question of what works best for the people who use public services is submerged beneath the question of who has won in a battle between ministers and public servants. It kills reasoned argument. What data there is on the allegedly lethal effects of weekend NHS understaffing, or on the relative performance of academies and local authority schools, has already been tortured into confessing support for both sides of the argument. The politics of confrontation is grinding compromise into dust.

It was the prospect of constructive engagement across partisan lines that once made coalition seem exotic and, to a non-tribal audience, appealing. This is not meant as some floral tribute at the Lib Dems’ electoral graveside. They swapped the moral high ground of opposition for the mucky trenches of power, traded away too much of what they had stood for, and were buried.

So it goes. Yet they did, briefly, represent an ethos of civilised collaboration. Coalition required a modicum of generosity in imagining that political rivals might have a point, or that their motives might not be entirely vicious, or even just that there were individuals in other parties with whom constructive business could be done. It didn’t last. That spirit expired last summer. Cameron won his majority; Labour chose a path of no compromise. Two tribes in perpetual antagonism. That is what matters, apparently. What a shame it doesn’t work.