By the time Mitt Romney formally launched his bid for the US presidency in late summer 2012, the race for the White House was already more or less over. For the preceding 12 months, the former Massachusetts governor had poured all his energy into securing the Republican nomination from his conservative rivals, leaving the Democrats free to bury his reputation as a successful entrepreneur under a volley of personal attacks. These attacks cast Romney, not entirely inaccurately, as a predatory capitalist whose business practices at Bain Capital had put thousands of ordinary Americans out of work or into bankruptcy. The result was that in the weeks leading up to 6 November, Romney spent more time fending off accusations that he was ‘out of touch’ than he did explaining his policies or scrutinising Barack Obama’s record. Romney’s mistake was to allow his public image to be defined negatively by his opponents before he had a chance to define it himself.

A comparison can be drawn between Romney’s experience and the situation Scotland’s pro independence movement currently finds itself in. Since the launches of the official 'Yes' and 'No' campaigns last year, the unionists have been far more effective at setting the terms and conditions of debate than the nationalists have. On a series of issues, most notably the currency and (until yesterday) Scottish membership of the European Union, Better Together, the official vehicle of unionism, has forced the SNP onto the back-foot. Time and time again, Scottish government ministers have been rushed out to provide what seem like hurried or improvised responses to awkward questions. With his relentless emphasis of the apparent "risks" and "hazards" of separation, Better Together chairman Alistair Darling has become an almost ubiquitous presence on Scottish TV screens. Darling’s rhetoric reflects the No camp’s key theme: that the consequences of Scotland leaving the United Kingdom are uncertain and uncertainty is bad for the Scottish economy.

With at least two recent polls showing a decline in support for independence, there is good reason to believe this strategy is working. The unionists have an additional advantage in the fact Scottish political culture is dominated by an essentially conservative middle-class with little enthusiasm for far-reaching constitutional reform. Worse still for the Yes campaign, the Scottish government doesn’t intend to publish its White Paper on Independence, clarifying its proposals for an independent Scottish state, until the end of the year. This grants Better Together yet more time in which to compound voters’ anxieties, increasing the likelihood that, come the final stages of the referendum debate, it will be too late for the SNP and its allies to rescue independence as a credible constitutional option in the eyes of the Scottish electorate.

There is another reason the pro-independence movement has struggled in the referendum PR battle: a lack of structural discipline. Although the majority of Yes Scotland activists are members of the SNP, the organisation itself is made up of a broad coalition of groups, each with their own ideas about how independence should be achieved. To some extent, this laissez-faire style acts as a source of creativity, generating new initiatives, like the Radical Independence Conference, and genuine excitement at the grassroots level. (600 people attended the launch of Yes Glasgow earlier this month.) But it also makes the task of developing a coherent message about independence extremely difficult. By contrast, Better Together is a considerably smaller and less cumbersome outfit, with a much more tightly controlled and clearly defined narrative. Its role - to erode trust in Alex Salmond and reinforce widespread concerns about secession - is relatively uncomplicated.

So how might Yes Scotland regain the initiative? A more effective Yes campaign would balance its aspirational account of Scotland’s ‘journey’ from devolution to independence with a critique of the British state, highlighting the democratic and international costs Scotland pays for remaining part of the UK. In particular, it would make clear the link between Scotland’s abysmal social record (one of the worst in western Europe) and the concentration of political and economic power in London and the south east. It would also aim to systematically undermine the Scottish public’s confidence in the desire and capacity of Westminster to act in Scotland’s interests, even if this means abandoning its much vaunted commitment to positive campaigning. The one thing it can’t afford to do is spend the next 20 months responding to aggressive unionist and media questioning.

Of course, it was the use of exactly these sorts of ‘negative’ tactics that secured Obama’s second presidential term. Recognising that the circumstances of the 2012 election were going to be very different from those of the 2008 one, Obama and his team discarded the transformative rhetoric of "hope" and "change" for a harder, more cynical approach, turning what should have been Romney’s greatest asset - his commercial success - into his greatest weakness through a sustained media offensive. Likewise, the SNP needs to acknowledge that the 2014 referendum will not be a re-run of its 2011 electoral triumph, when it bulldozed its way to victory on the back of what one commentator called a nationalist "juggernaut of joy." The independence vote will take place against a backdrop of high unemployment, recession and austerity imposed by a discredited and corrupt Westminster class increasingly at odds with Scottish political values and preferences. There is a deep well of political dissatisfaction in Scotland: advocates of independence need to learn how to exploit it.