If the SDLP strategy is as described here, it is an extraordinary combination of complacency and bad mathematics. If SF are good at one thing, it is minimising the difference in votes between candidates to get as many as possible elected under the single transferable vote. Other parties can aspire to this from time to time (the SDLP snatched a seat in East Londonderry in 1998 in this way, and also benefited from the failures of DUP, UUP and Alliance to balance in East Antrim) but it’s very difficult to plan for.
Anyway, I wonder how many Unionist voters truly care whether the SDLP or SF ends up as the largest party? It seems to me most unlikely that enough Unionist voters will see the SDLP as the critical bulwark against SF victories. Those who are really hostile to SF will be not much less hostile to the SDLP, and unlikely to give them lower preferences.
There *is* evidence of some Unionists voting for the SDLP in South Belfast in 2001, but that was to oppose Martin Smyth not to oppose SF. Also it’s true that Danny O’Connor won his East Antrim seat in 1998 on UUP transfers, but that was in a situation where he was trying to outpoll the DUP’s Jack McKee rather than SF.
Looking at the SDLP’s four target seats: in Strangford and North Down it’s difficult to see where their optimism comes from; there is no evidence that their vote has increased since 1998. In South Antrim it’s difficult to believe in a second Nationalist seat, though if Alliance’s support were to collapse the SDLP would be best placed to pick up (same is true of Strangford). In North Antrim they need improbably tight vote management combined with a decline in SF support (for which there is no evidence).
As for the vulnerable SDLP seats, we can forget about the two losses to SF in East Londonderry and (probably) West Tyrone, sufficient on their own to make SF the larger Nationalist party. The most interesting ones are those which might fall to Unionists in Lagan Valley, East Antrim and West Belfast. The first two of these also have ex-UKUP seats ripe for the plucking. I suspect that these will be the crucial battlegrounds that decide the DUP/UUP struggle.