Hanging out
With today's , the SNP and their Welsh chums Plaid Cymru are trying to turn a potentially weak position into one of relative strength.
The weakness is that, by dint of simple arithmetic, neither the SNP nor Plaid can win the UK General Election in the conventional sense of seeing their leader entering Downing Street as Prime Minister.
That prompts rival parties to claim that the Nationalists are irrelevant in a UK contest, that the voters should, as a consequence, disregard their appeal for support.
So how to turn that round? By positing a hung parliament - and suggesting that a bloc of SNP and Plaid MPs would be able, in such circumstances, to extract substantial concessions for Scotland and Wales.
By this device, the Nationalists argue that their leaders would indeed be able to enter Downing Street - as invited visitors, to negotiate a deal in the interests of their respective nations.
Today's launch suggests that the two parties would be looking for "fair funding for Wales and Scotland" plus protecting local services, action to help the green economy and support for housing growth.
The document suggests that both would seek to replace the current Barnett formula which determines spending in Wales and Scotland by comparison with changes in relevant English departmental budgets.
Spending advantage
Of course, many English MPs have long regarded Barnett with loathing (the formula, that is, not Lord Joel Barnett who devised it.)
They regard it as feather-bedding the Scots and the Welsh, entrenching higher spending levels.
By contrast, Nationalists in Scotland point to the fact that Barnett is and was designed to be a convergence mechanism, progressively squeezing Scotland's historic spending advantage.
In Wales, Barnett is cordially disliked.
So, for Scotland, the "Celtic Alliance" would seek fiscal autonomy. For Wales, they would seek "fairer funding". Translation: more generous.
It is all eerily reminiscent of the earlier claim by Gordon Brown that his Labour party offered investment while the Tories promised cuts.
Mr Brown finessed this when the extent of the potential spending crisis made this difficult to sustain.
'Disadvantage to gain'
But, of course, the SNP and Plaid don't have to spell out a UK spending programme of their own.
They merely demand concessions from the parties seeking UK power. Again, their relative remoteness from that UK power is turned, they hope, from a disadvantage to a gain.
Problems? Of course. Rival parties will say that the programme is thoroughly unrealistic, given the condition of the accumulated deficit.
The Nationalists will reply that they are entitled to stand up for their own nations' interests.
Further, will the Celtic Alliance be in a position to bargain. Will there be a hung Parliament? Will they win enough seats to get, potentially, to the table?
If they do, will the UK leaders negotiate with them? Or would, say, the Tories prefer to strike a deal with the Liberal Democrats or parties in Northern Ireland?
Challenges ahead. Potentially.