Usually, this is a line trotted out to avoid discussing a difficult matter – failings in the health service, say, or falling standards in schools.

But, occasionally, what they say is true. Some issues really are too important to play politics with.

To her credit, First Minister Nicola Sturgeon recognised last week that the poisoning of a former Russia spy and his daughter in Salisbury is one such case. This is a national security issue affecting the entirety of the United Kingdom and Sturgeon was the stateswoman the moment demanded.

Nicola Sturgeon urged to take action over SNP NEC member’s role on Salmond show

After Prime Minister Theresa May announced that Russia was being held responsible for the nerve agent attack on 66-year-old Sergei Skripal and his 33-year-old daughter, Yulia, and that 23 of Vladimir Putin’s diplomats were being expelled from the UK, the First Minister spoke to the media. And she had no interest in “playing politics” with the issue.

Sturgeon fully condemned Russia over the outrage and offered her full support to the PM. It was very clear, added the First Minister, that Russia could not be permitted to kill or attempt to kill people on the streets of the UK with impunity.

This will have come as a huge relief to those who grow weary with the SNP’s usual tactic of making any and every issue about the failure of the UK. There are many among the SNP’s supporters who would have been perfectly happy to hear the FM say the attack was a “chickens coming home to roost” scenario. Fortunately, Sturgeon was to disappoint them.

The former first minister on Russia Today, the propaganda arm of the Kremlin, on which he said he enjoyed full editorial independence

But while the First Minister may have promptly marched her party to the right side of these bleak developments, the SNP still stands to be damaged by them.

As is increasingly the case these days, responsibility for damage to the Scottish nationalists’ cause lies with its former leader, and Sturgeon’s predecessor as first minister, Alex Salmond.

While Sturgeon faced the cameras, supporting the PM, Salmond was preparing for the latest edition of his weekly political chat show on the Kremlin-funded propaganda channel, Russia Today – or RT as it now brands itself.

As Sturgeon stood up for the values we share across these islands, Salmond bent the knee to Moscow, parroting the line that RT was a perfectly legitimate broadcaster and insisting that he was free to say whatever he wanted during his half-hourly programme.

The matter of Salmond’s editorial independence (which doesn’t stretch to the news “ticker tape” that runs across the bottom of the screen, pumping out pro-Russian propaganda during every programme) is a mere detail in a far bigger picture, one that shows the former first minister as, at best, a dupe, a useful idiot.

RT is funded by the Russian State with the twin objectives of peddling the Kremlin line on sundry matters and undermining the positions of western governments. It is not a broadcaster in the style of the BBC but President Vladimir Putin’s personal department of (mis)information.

Asked about Salmond’s continued involvement with RT, Sturgeon said she had not changed her previously declared view that her former boss should not be working for it. But Alex is a private citizen, you see, so there’s not much more she could say or do…

This is a problematic position. Yes, it is true that ex-politician Salmond is no longer an elected representative, but to suggest that he is now little more than a bloke in the street is a nonsense.

Salmond is – and will remain until someone leads the nationalists to a referendum victory – the most famous and influential figure in the SNP’s history. The party would not be where it is now, enjoying a third term in government at Holyrood, without the work he did after returning in 2004 for a second stint as leader. Sturgeon would not be First Minister without Salmond.

Among those closest to Sturgeon, anger at Salmond’s continued association with RT is palpable. He is, says one senior nationalist, a “f***ing disgrace”.

There’s anger, too, at the role of Salmond’s business partner, Tasmina Ahmed-Sheikh, who produces his grubby little RT show. She may have lost her Westminster seat in last year’s general election but she remains a national office bearer with the SNP. As Convener for Women and Equalities, she sits on the party’s national executive. She is most assuredly not merely a private citizen when it comes to the SNP.

Wise heads at the top of the SNP say that Ahmed-Sheikh cannot continue to be an office bearer while also working for the Russians. As one SNP politician put it to me “Russia? Equality? You’re having a laugh.”

The chemical attack in Salisbury is an agenda-changing moment. Serious politicians from across the spectrum are united in condemnation of an act of barbarity.

Against this backdrop, Salmond is no longer the SNP’s greatest hope, he is the source of its continued embarrassment.

The former first minister may not take dictation from the Kremlin before each show but, then, he doesn’t have to. His appearance on RT helps create a veneer of respectability to an organisation that isn’t about truth but about twisting reality to suit Putin’s objectives.

The incident in Salisbury could just as easily have taken place in Perth or St Andrews. Scotland is not immune from this sort of outrage. While Sturgeon clearly grasps this, Salmond either doesn’t or does but doesn’t care.

The SNP can safely bank on the support of those who view Salmond as great political leader. Those who answered his call to support Scottish independence remain steadfast.

But others – including some of those the SNP must persuade to change their minds if a future referendum is to be won – will surely look at his behaviour and wonder whether the SNP is the great progressive, moral force it claims to be.

Alex Salmond may be a “private citizen”, but his continued employment by RT isn’t good for either his party or his country.

Euan McColm: Alex Salmond TV's hard viewing after Salisbury watershed