TELL me what you see. Nicola Sturgeon and Alastair Campbell, obviously, but what else? Maybe you’re feeling pretty positive about the picture and see it a sign of the broad coalition that’s building in favour of a second EU referendum (the photograph was taken at the People’s Vote protests in London). Or maybe you see something different. Maybe you see the leader of an apparently progressive independence movement posing for a selfie with a man involved in the promotion of the calamitous Iraq War. It’s funny how we can all be looking the same way and see something different.

Certainly, the picture of Mrs Sturgeon and Mr Campbell has gone down very badly indeed with some Scottish nationalists, particularly those on the left. Jonathon Shafi, the co-founder of the Radical Independence campaign and a columnist in The Herald, described the photograph as sickening and said the SNP would never get his vote again as long as Mrs Sturgeon was leader of the party. Other nationalists made similar comments, although some said the picture was nothing more than a quick selfie and “just a picture”. What’s wrong, they said, with political figures coming together to promote a good cause?

My answer to that would be “nothing” but even so, the selfie of the former director of communications for Tony Blair and the current First Minister is still a political curiosity. Take Mr Campbell first. There he was, on the 23rd of March 2019, enthusiastically taking part in a protest against an unpopular policy, but compare that to the 15th of February 2003 - the day, you may remember, of the protests against the Iraq War. Writing in his diary that day, Mr Campbell complained about what he called the uncritical coverage of the event. He also said this: “I bumped into no end of people coming back from the march, placards under arms, faces full of self-righteousness.”

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So what, I wonder, was that showing on Mr Campbell’s face on Saturday when he posed for the selfie with Nicola Sturgeon: self-righteousness or just a change of heart? And wasn’t there also something a bit weird about Mrs Sturgeon’s presence? The SNP campaigned languidly at best for Remain and was a late-late-late comer to the campaign for another vote on the EU and yet Mrs Sturgeon spoke as if she’d been a believer all her life. There are also contradictions in the First Minister’s belief in the power of protest – several big marches have been held in Scotland in favour of a quick referendum on Scottish independence, but Mrs Sturgeon has been deaf to their calls. Some marches are better than others.

For some left-leaning nationalists, the troubling/heartening picture of Mrs Sturgeon with Mr Campbell is also symbolic of where she’s going wrong with the strategy on independence. Instead of being radical and aggressive and anti-establishment, she is being cautious and conservative and is cosying up far too much to the establishment and what they would call the neo-liberal consensus. Their evidence? Item one: the Growth Commission report. Item two: the lack of a second independence referendum. Item three: a picture of Mrs Sturgeon with Tony Blair’s right-hand man.

I wonder, too, about what else was happening on Saturday: did the First Minister agree to take part in the People’s Vote march in the pretty certain knowledge that it would not succeed? Because that, sadly, is the fate of most protest marches unless a number of critical factors are in place - which in the case of the People’s Vote march, they aren’t.

Firstly, a march or protest has to appeal beyond the marchers and protesters to create any kind of momentum – it has to resonate for more than just the core supporters – and, despite the hundreds of thousands of people in London at the weekend, the polls show that the wider public is still pretty split on the idea of a second referendum; there’s also no evidence yet of a big enough consensus in Parliament to win a vote. And even all those signatures on the famous petition supporting a second referendum – all five million of them – will not be enough because five million is not as many as 17 million, the number who supported Leave.

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Secondly, to succeed, a march has to have support from the key political players and again, the People’s Vote movement doesn’t. It’s quite clear that any move for a second referendum in Parliament will not succeed unless it has the full-hearted support of Jeremy Corbyn, but the leader of the Labour party wasn’t there on Saturday. You could also argue that the same applies to all those marches in the summer for another Scottish independence referendum – until Nicola Sturgeon supports them, they might as well march to Timbuktu.

So why do it? Why write your message on the back of a bit of cardboard and march down the street? Partly, it’s about the atmosphere – there’s nothing quite as nice as being with lots of people who agree with you, although it can lead to some false assumptions. A lot of people marched for a second referendum on Europe at the weekend, but there isn’t a convincing majority for it among the public. Equally, a lot of people have marched for a second referendum on Scottish independence, but a majority of Scots don’t want it. But, to the sound of whistles and chants, the marchers make the mistake of overestimating the extent to which their views are shared by others.

Where there is hope for marchers of all kinds is in the longer term. The protests in 2003 that Alastair Campbell disliked so much may not have stopped the Iraq War, but they were part of the shift in perceptions that ended Blair’s premiership and the same can apply to other protests. Marchers may chant “We want change. When do we want it? Now” but perhaps an immediate change in policy is not the point as a protest can be part of changing public opinion long-term to the point where the government agrees to change or voters change the government.

Sadly, the People’s Vote campaign - despite all the people, despite all the speeches and despite that smiling selfie of Nicola Sturgeon and Alastair Campbell – is unlikely to pass this test. Long-term isn’t an option for this protest. It simply doesn’t have the luxury of time.