Nick Clegg will urge the Liberal Democrats to "tear off the rear view mirror" in a rally to open the party's spring conference in Gateshead this evening. It is a curious metaphor that is meant to signal optimism and determination - looking only at the governing road ahead, not nervously behind at the hard path already travelled. It could also be interpreted as denial.

The message will be reinforced by party chair Tim Farron, whose speech is previewed in a Guardian op-ed this morning. He invites Lib Dems - instructs them even - to stop feeling guilty about the compromises that have been made for the sake of coalition. Farron describes power as "an occupational hazard" for serious political parties and one from which the Lib Dems ought not shy away.

This coordinated message is meant to signal the fact that, as one strategist put it to me recently, "the party is coming out of its defensive crouch." There is cautious confidence that this May's local elections will not be a repeat of last year's massacre. Campaign resources are being more strategically focused; recent council by-election wins give grounds for optimism.

Meanwhile, Lib Dem MPs, most activists and Clegg himself are all fed up with the expectation that they ought to be apologising for the very fact of being in a coalition when, from their point of view, that is an epic achievement. What, after all, would have been the point of all those years in opposition if the chance to enact party policy had been turned down? The challenge, according to this analysis, is to explain to a sceptical and inattentive public quite how much Lib Dem policy is actually being introduced and what a triumph this is, making the country fairer; or fairer, at least, than it would have been had the Tories been able to rule unrestrained.

And there lies the biggest problem. Partly by necessity, partly through ill-judgement, the Lib Dems have ended up winning many little things, while the Conservatives have won very big things. The two defining issues of this parliament could well end up being George Osborne's economic choice to press ahead with austerity at an accelerated pace and David Cameron's decision to forge ahead with unpopular and poorly understood NHS reforms. Labour are convinced the public will turn against both. (The evidence only supports that assertion with regard to the health service.) Either way, the Lib Dem role is cast firmly as accomplice, which is the classic trap for junior coalition partners - maximum pain if it goes wrong; minimum credit if it works. The "pupil premium" and tweaks to the House of Lords won't alter that equation much.

Lib Dems gathering in Gateshead today know that much, which is why they are agitated about the Health and Social Care Bill. This time last year, a rebellious mood at the party's spring conference helped spur Clegg into demanding a "pause" in the legislative process to reconsider the whole thing. There is a growing sense in the party that the reforms have not changed enough (or are not judged to be anything other than trouble by the public) to justify endorsement. Would not the Lib Dems be able to signal their true worth in government by vetoing the measure altogether? Might they not then be able to campaign on a claim to have saved the NHS? To that end there is a motion in the works - yet to be scheduled for debate - calling for the health reforms to be scrapped.

Senior Lib Dems (and a large number of Tories, including some close to Downing Street) wish Clegg had killed the bill last year. Instead, the reforms have been mangled enough by constant amendment to persuade the public that the whole thing is a shambles, but not enough to convince anyone that the underlying intent has been changed. This is, without doubt, a disaster for the government.

David Cameron hopes that, once the furore around the actual legislation is out of the way, a process of explanation, education and reassurance can reconcile people to the changes. The one person in politics best equipped to know how wrong that assumption is should be Nick Clegg. It is exactly the technique he tried after his party's u-turn on tuition fees. (One reason to hold on to that rear view mirror for a while, perhaps.) He explained over and over again how the new system was, in fact, fairer than the old one, how it was the best option available, how the underlying principle that had led him to make his anti-fees pledge in opposition was kind of honoured by measures being taken to mitigate ... blah, blah. No matter.

A visceral sense of betrayal created an emotional barrier that no rational argument could penetrate. There is a danger of the same happening with the NHS. Once people decide that Cameron and co. have reneged on a fundamental pledge to protect the health service, they aren't going to be swayed by a claim that cuts and chaos are a different kind of protection - special long-term protection that requires pain in the short-term. Anger is rarely appeased with a graph. And, of course, when that happens, Clegg's amendments, adjustments and moderations will be worth nothing. No one thanks the midwife at the birth of a monster.

This problem expresses a wider strategic challenge for the Lib Dems - and for Clegg in particular. The party is having to work out how to make coalition government work and educate voters about what that means at the same time. It also has the misfortune to be allied with the Tories, who aggravate a unique kind of hostility among a section of the population whose votes Clegg needs. That distaste is deep-rooted and cultural; it transcends day-to-day politics. This tribal barrier is not unique to British politics, but it is especially pronounced by European standards. Clegg's sense of how coalition ought to be part of the Westminster repertoire is derived, in part, from his experience of the continent.

He is taking the Lib Dems on a transition from being one kind of party to something completely different. He took over something distinctly British, mildly eccentric, contrarian, and comfortable in opposition and is turning it into a technocratic, professional party of coalition. It is like remodelling the Campaign for Real Ale as McKinsey. Tricky.

The most compelling argument for what Clegg is trying to do (leaving aside how effectively he is managing it) is that there is no alternative. A party that refuses the opportunity to govern forfeits the right to be taken seriously. But given the Lib Dems' poll ratings, the grass roots could be forgiven for wondering how much more pain they have to endure before the political dividends of the transformation are felt. On this journey it isn't the rear view mirror Clegg has to worry about, it's everyone in the back chanting "are we nearly there yet?"