RARELY can Alex Salmond's breakfast reading have been so indigestible: EU Liar, Eu're a Liar Mr Salmond, Bruised Salmond denies lying as rows engulf SNP, Salmond on rack in SNP's worst day.

The newspaper headlines which greeted the First Minister on Wednesday morning were the most uniformly hostile since he took office in 2007.

Even during the release of the Lockerbie bomber and long-forgotten rows over Donald Trump's golf course, Salmond received mixed reviews. But the admission that SNP ministers had never had official legal advice to support their longstanding case that an independent Scotland would automatically be in the EU and avoid the Euro changed all that.

The fact the Government had launched a court action, at a cost to taxpayers of £12,000, to avoid admitting it earlier added to the scorn and provided a field day for the opposition.

Citing a recent BBC interview in which the First Minister seemed to say legal advice did exist, Labour felt sufficiently emboldened to call him "a barefaced liar" and ensured lurid coverage.

With the uproar about non-existent advice coming on the same day two MSPs quit the SNP over Nato policy, shaving its Holyrood majority to two, the term "scomnishambles" was coined on Twitter to try to convey the sense of mounting crisis.

The pro-Union parties proclaimed the SNP's case on Europe had unravelled, and asked what else the SNP were confidently asserting about independence without solid evidence to back it up.

At First Minister's Questions on Thursday, Labour leader Johann Lamont hammered home the point.

This wasn't just about the EU, it was about trust – trust in Salmond and trust in his key policy.

"How can this country have an honest debate about our future when we cannot trust a word that Alex Salmond says?" she said.

But are Labour and the other pro-Union parties confusing a lousy few days for the SNP with a game-changing moment in the referendum campaign? After all, a recent poll found 71% of Scots put most trust in the Scottish government to act in the country's best interests, compared to 18% placing their faith in Westminster.

A senior SNP insider is cheerily dismissive. "Labour say trust is an issue, so they've tried to shoehorn the events of the week into that frame, but for most people it was an arcane process issue – it didn't resonate.

"We're happy to focus on trust because there's a lack of trust in a Westminster government which imposes welfare cuts and can't manage the West Coast main line. That impacts on people's lives." Yet Labour are sure that "trust" is the chink in Salmond's armour and thanks to it they've found the over-arching theme of the referendum, one that can be adapted to almost any issue over the next two years."

Sources say the party's private research has identified Salmond's "trust issue" as one of his greatest liabilities with voters.

Where Lamont is seen as "authentic" and "honest", Salmond is seen by many people as neither.

Now Labour, the driving force behind the Better Together campaign for a No vote in 2014, intend to turn that chink into a crevasse.

If they can discredit the messenger, they can discredit the message, goes the theory.

It is not meant to be pretty – calling Salmond a liar shows that – but they think it can work.

"Trust is an issue," said one Labour

strategist. "People say, 'Oh yes, Salmond's a decent, big figure' but they don't really trust him. And in the independence debate, the message-carriers are important. So we're pushing hard on that.

"But it's also Europe. If you say independence equals the euro, support for it plummets. And this week every newspaper said he was a liar on the subject."

By itself, the EU row is unlikely to cause much damage – much of the argument has already sunk into semantics – so Labour are hoping for a cumulative effect, with the SNP made to back down on a series of past claims about independence.

In this, the pro-Union side is abetted by Salmond's habit of making cast-iron statements about things which are not wholly cut and dried.

Even though he may have strong arguments and common sense on his side, all too often the First Minister skips the caveats and says such and such will be the case, no doubts, no contest.

And then, slowly, it turns out that, as in the EU case, life is more complex, and he has to go through contortions to finesse his position.

In day-to-day politics that can be awkward. But in the independence debate, the high stakes mean every wobble is magnified into a calamity.

Expect future rows over Salmond's assertion that an independent Scotland can keep the pound without a stability pact with London, and the claim Scotland and the rest of the UK will share a common system of financial regulation, which financiers say is plain illegal under EU law.

The subjects might be anoraky, but if Salmond is shown to have made inflated or poorly evidenced statements about enough of them, Labour reckon it could build a damaging impression, and in politics perception is what counts.

It's not just Labour thinking about trust. Some in the SNP are keenly aware that if the party leader looks bad it will be harder to secure the larger prize of independence.

"There are trust issues," admits a senior SNP figure. "There is no proof or evidence for a lot of the things that have been said.

''Trust also came up at the local elections – Alex's meetings with Rupert Murdoch. People might have Sky in their house but they don't like politicians cosying up to big business people."

Besides foregrounding trust, the week was also a reminder that the Salmond magic cannot last indefinitely. There was a whiff of political mortality in the air.

Told that Tony Blair would serve a third term as Prime Minister instead of handing over to his Chancellor, Gordon Brown reportedly wailed: "I've already had seven years. Once you've had seven years, the public start getting sick of you - After that, you're on the down slope."

BY the time of the referendum, Salmond will have been First Minister for seven-and-a-half years.

For now, his 50% personal approval rating is stratospherically high for a second-term leader. None of his opposition peers is higher than 35%, while Nick Clegg is a wretched 23%.

But since the start of the year and the hotting up of the independence debate, Salmond's net satisfaction rating – the difference between those approving and disapproving of how he does his job – has nosedived. Last December it was plus 35 (62% satisfied against 27% dissatisfied), but in January it was +22, in June +13, and this month it's +10.

Again, Salmond is far ahead of his peers. Johann Lamont is +5 while David Cameron is -29.

But Mark Diffley, director of Ipsos MORI Scotland, whose Scottish Public Opinion Monitor compiles the figures, senses something afoot.

"There's been a considerable slip," he said. "You would expect the gloss to come off at some stage. But there does seem to be something going with his ratings and support for independence and support for the SNP [all down recently].

"He's still more popular than either independence or the SNP. So in that regard he's clearly still a huge asset. But it's whether any of this rubs off and makes people feel differently about him. He's going to be the figurehead of the campaign. You can understand entirely why [other parties] would look to attack him personally."

Salmond may have survived last week's furore, but like every politician he has a shelf life. The big question for the SNP and the independence movement is whether it extends to October 2014.