POLITICALLY, Scotland is different. A former state, a former kingdom, still palpably a nation, with an enduring debate anent its constitutional future.

A discourse which sometimes roars and sometimes susurrates. But which forms the fundamental fault-line in Scottish politics.

The Scottish National Party is also different. A movement, a cause, rather than simply a party in persistent pursuit of votes and power.

Different, but not immune. The SNP remains vulnerable to internal conflict. To moments when its prime advocates only open their mouths to change feet.

Such is presently the case. The leadership contest has, bluntly, damaged the SNP’s public standing and also, perhaps, the cause of independence.

Read more by Brian Taylor: A new leader for the SNP. So what will change?

It is, in truth, difficult to measure the precise extent of the damage to that wider cause – although at least one poll has suggested a drop in support.

Maybe, in search of enlightenment, we should consult Ash Regan’s “independence readiness thermometer”.

Not heard of that? I think it is in Scotland’s capital, right next to the central bank preparing for a Scottish currency within a couple of months of ending the Union.

Then there are the comments by Humza Yousaf, suggesting that his principal opponent, Kate Forbes, is deterring Yes voters because of her moral stance on such matters as equal marriage and gender reform.

Mr Yousaf says he means to implore, rather than chide – and Ms Forbes says she would not allow her faith to govern Scots Law on issues of equality.

I am told by insiders that Kate Forbes discounted advisers who said she should ca’ canny over those early moral sentiments, who said she should moderate and modulate her stance.

That policy, which she calls “robust and frank”, has persisted.

HeraldScotland: Humza Yousaf, Kate Forbes and Ash ReganHumza Yousaf, Kate Forbes and Ash Regan (Image: free)

In the STV debate, she chose to open her cross-examination of Humza Yousaf by rubbishing his Ministerial record in every portfolio he has held, from transport to justice and now health.

This was, therefore, calculated and planned. Not an obiter dictum, in the heat of debate.

What on earth possessed her? Did she not envisage the gleeful grins of her party’s opponents? Did she not anticipate that Douglas Ross would promise to put her words on every Tory leaflet?

OK, she wants to win this contest. That may mean a few sharp words. But this attack encompassed the very government in which she has apparently been content to serve.

Cue, as noted, subdued chortling from the SNP’s opponents. Labour detects an opportunity.

The Liberal Democrats, conferring in Dundee this weekend, spot a chance. Even the Tories, struggling over UK economic travails, have been buoyed.

And Nationalists? They are, frankly, despondent, despite the ebullient banter aimed by the First Minister at Douglas Ross.

Read more by Brian Taylor: New SNP leader will need to pursue a new direction

One MSP told me it was like a conflict in the family. Another noted that social media amplified the bile on display. A third spoke of bitterness in private discussions.

Mhairi Black, the party’s deputy leader at Westminster, was asked if the SNP could split – and replied that she did not know at this stage.

Now, a few words of caution. This is mid-campaign. Ms Black was seeking to warn fellow SNP members against endorsing Kate Forbes. This was electioneering, not analysis or a forecast.

Further, the Channel 4 debate was a little more subdued – although Ms Forbes complained later that Mr Yousaf had sought to pursue her over faith issues. Ms Regan appealed for an end to personal attacks.

There is another point, which bears repeating. The SNP is different. It is a cause, not just a party.

That is the SNP’s strength. It creates a patriotic bond which surmounts mere politics. It generates internal loyalty. Members defend their party largely out of self-discipline, not imposed control.

However, it is also the SNP’s weakness. It means that there are few ideological pillars in common upon which to construct a sound and lasting political edifice.

Folk join the SNP because they favour independence. They also support standing up for Scottish interests. Beyond that, they may be indifferent – or in need of persuasion.

Such has been the SNP’s history. A movement founded upon a sense of Scottish identity has evolved into a moderately left of centre party with a focus on progressive taxation and redistribution.

Those characteristics, however, are reactive, rather than intuitive. They derive from Scotland’s demography – and from the prompting of successive, recent leaders.

Now, all parties have their internal combats. All are coalitions of the more or less willing.

But the SNP’s bond remains independence. Not social or economic policy. Hence, I believe, the magnified problems which can arise when a particular issue sits ill with sections of the membership.

To repeat, though, that fundamental common purpose of independence can be the SNP’s strength. In this contest, it may foster eventual unity – or, at least, regrouping – in the aftermath of evident bitterness.

That may depend, of course, upon outcome. The departing leadership seemingly favour Mr Yousaf.

Nicola Sturgeon has depicted Scotland as socially liberal and, this week, listed policy achievements which coincided with Mr Yousaf’s remits.

Doubtless, shortage of time, enforced by prompting from the chair, prevented her from mentioning Ms Forbes’ endeavours in office.

Insiders say it could all hinge on those who support Ash Regan. Where do her second preferences go? The common presumption is that they would shift to Kate Forbes, if they are disquieted with current SNP strategy.

Either way, there will be the strong pull of unity, driven by the common cause of independence.

Down the decades, sundry Westminster politicians have frequently failed to comprehend that dimension in Scottish politics. Or, at least, to grasp it fully.

Not just Scotland, of course. By chance, I am close to finishing Roy Jenkins’ outstanding biography of Gladstone.

Jenkins recounts how the Grand Old Man wrestled with the Irish Question while, around him at Westminster, there arose layers of puzzlement, confusion and prejudice.

For the avoidance of any doubt, I am not remotely comparing present day Scotland to 19th century Ireland. Not for an instant.

It is, however, worth noting that, while nationalist parties may experience severe internal dissent, they also have a centripetal force field which can encourage reunification.

Perhaps that may happen in this instance. Perhaps.