Scottish independence: 'Invaluable second chance' for Alex Salmond
There is little doubt that the spotlight and the pressure will be on Mr Salmond in tonight's referendum leaders' debate.
Most voters reckoned it was his opponent, Mr Darling, who won the first leaders' debate three weeks ago.
ICM's instant poll of those who actually watched the programme found that 47% put Mr Darling ahead, while only 37% believed the first minister came off best.
When a week later ICM asked a sample of all voters who they thought had won, 42% felt that Mr Darling had done so, while only 19% were willing to give the verdict to Mr Salmond.
This was not the outcome the "Yes" side had anticipated or could afford. Still behind in the polls, it had hoped the debate would prove a fruitful opportunity to win converts to its cause.
However, today's second debate could still prove to be an invaluable second chance for Mr Salmond.
For although he may have lost out first time around, his performance does not appear to have done irreparable damage to the "Yes" side's prospects.
Of the four polls that have been conducted since the first leaders' debate, three have actually registered an increase in "Yes" support.
On average the "Yes" vote in these four polls was a point higher than it had been when the same four polls had previously been conducted in advance of the leaders' debate.
It is widely thought that the part of the first leaders' debate that secured victory for Mr Darling was when he grilled the first minister about his plans for the currency an independent Scotland would use.
However, it seems that voters are no more likely to be convinced now of the "No" side's arguments on this issue than they were when the chancellor, George Osborne, first announced in February that an independent Scotland would not be allowed to share the pound in a monetary union with the rest of the UK.
Shortly after the first debate, Survation reported that just as many voters (40%) believe that the "No" side are 'bluffing' on the currency issue as are convinced it is not (39%) - much as in February 37% believed it was bluffing and 37% not.
Meanwhile, according to ICM, 45% still believe that an independent Scotland would be able to use the pound in much the same way as it does now, little different from the 47% who were of that view in February.
Mr Salmond might have lost the first debate, but he and the "Yes" side are still in a position to try and put their case another day.
Job well done
Indeed, the first debate has provided a salutary lesson for all of the media who will be watching tonight's debate intently.
Even if one man does come out on top, this does not necessarily mean that they will have persuaded more voters of the merits of their arguments, let alone changed the way they intend to vote.
Rhetorical and inquisitorial skill is not necessarily the same as persuasive argument.
Still, even if Mr Darling's efforts first time around did not deliver his side many votes, he will still have regarded it as a job well done.
For, ahead in the polls, all that the "No" side needed to do then - and need to do tonight - is to avoid losing any ground.
On average (and once the "Don't Knows" are left aside) the "Yes" vote in the last six polls has on average been 43%, with "No" on 57%.
The polls have seemingly been stuck at more or less this figure ever since the beginning of April, just oscillating up and down a little but never showing a consistent trend.
True, the polls do not all agree with each other. Panelbase (average "Yes" vote since April, 47%) together with ICM (45%) and Survation (45%) paint a more optimistic picture for the "Yes" side than TNS BMRB (42%), YouGov (41%) or Ipsos Mori (41%).
But not a single one of these polls has ever actually put the "Yes" side ahead.
With just three weeks to go, Mr Salmond badly needs tonight's debate to move the polls in the "Yes" side's direction. It could well be his last chance to do so.
John Curtice is Professor of Politics at Strathclyde University and Chief Commentator at whatscotlandthinks.org, where a comprehensive collection of referendum polling data is to be found.