As Iain Duncan Smith and his Employment Minister Chris Grayling mount a robust defence of the government's work experience schemes, Nick Clegg is handing out the sweeties. Yesterday the Deputy Prime Minister announced a new £126 million initiative to bribe (sorry, incentivise) employers into finding jobs for 16 and 17 year olds with the worst GCSE results. The scheme itself is embedded in so much bureaucracy that the £2,200 per teenager offered to employers seems unlikely to be transformational. But it sits well with Mr Clegg's desire to be the nice guy, who always has some cash ready to soften the austerity of the government's programme.

Yesterday also saw a preview of the Liberal Democrats' latest party political broadcast, in which Nick Clegg emphasises that it's his party that plans to take the low paid out of tax. The older the coalition becomes, and the closer we move towards the next election (as well as a potential leadership challenge), the keener Mr Clegg becomes to differentiate “nice” LibDem policies from “nasty” Conservative cuts. So how is the good cop, bad cop routine working out for his poll ratings?

Not too well, according to the latest from Populus (in yesterday's Times) and the Guardian's ICM findings. Both pollsters note that Liberal Democrat support continues to fall and Populus finds that since last summer Mr Clegg's personal ratings have fallen most sharply amongst Liberal Democrat voters. As the Times's Sam Coates observes, this precipitate decline coincides with the period in which Mr Clegg has sought to talk up the differences between Lib Dem and Conservative policies. The tactic does not seem to impress Lib Dem supporters any more than voters at large.

ICM's poll questioned the public about the NHS reforms and found more dismaying results for Mr Clegg to digest: when it comes to the health service, his party is even less trusted than the Conservatives. Only 9% think the Liberal Democrats can be trusted “a lot” with the NHS, compared to the Conservatives 13% and Labour's 23%. The Deputy Prime Minister's claims to have extracted important concessions on the health bill, and noisy interventions by Liberal Democrat peers led by Shirley Williams, have either failed to impress or simply escaped the voters' attention.

Speaking of noisy interventions, another notable finding from Populus is the extent to which Vince Cable's popularity has slumped in recent months; amongst all voters his rating have fallen by 5.5 points – almost as fast as poor Ed Miliband's. On present polling trends, Dr Cable's victory in appointing Les Ebdon as university access tsar in the face of Conservative opposition will do nothing to enhance his popularity and may instead damage him further.

All this points to a long term problem for the Liberal Democrats, which they show no sign of mastering. Never having governed alone, and with no prospect of so doing, the party has historically been reliant on defining itself against the two larger parties, thereby gathering up the protest vote. To this was added the luxury of cooking up unaffordable policies which were never expected to see the light of day, the abolition of university tuition fees being a prime example.

In the summer of 2010, by deciding to sign the coalition agreement, Nick Clegg relinquished the opportunity to contrast his party agenda with that of the Conservatives. It must have seemed like a good trade off: the spoils of office, ministerial jobs for nearly half of his MPs, and a chance to implement a decent number of Lib Dem policies. Indeed, if the Quad is anything like as powerful as James Forsyth has claimed, the reward for Nick Clegg and Danny Alexander has been to provide them with a disproportionate degree of influence. Having taken the plunge into power-sharing with the Tories, Mr Clegg's best prospect was surely to focus on the commitments set out in the coalition agreement and to convince the public that this new and consensual way of governing was better than single party rule?

But as Tim reported on Sunday, the experience of being governed by a coalition has left voters disenchanted; most people would now prefer to have a single party in charge. And the biggest losers from the apparent failure of this experiment are, of course, the Liberal Democrats. Because if, as it now seems, they have not succeeded in persuading the voter that power-sharing is the way ahead, then what reason is there for the continued existence of this third party?

As the Deputy Prime Minister now seeks to disassociate himself from coalition policies in an attempt to rebuild a distinct Liberal Democrat identity, he seems to be overlooking this awkward fact. If the Liberal Democrats are no good at being team players, then why vote for them at all?