Many seats need 30%+ of voters to vote tactically to beat the Tories. Huge numbers! Difficult but not impossible.
But we can't ignore the Meatloaf problem. ("I'd do anything for love, but I won't do that."
But many *would* vote LibDem as a last ditch option to stop Boris Johnson's brand of Brexit.
Why? LD politics are "closer" than Labour's, no Corbyn, past coalition.
Say...
Tory 45%
Labour 30%
LibDems 22%
Labour can persuade up to 22% of voters (need 15%+)
LD can persuade up to 75% of voters (need 23%+)
- Get 15% out of 22% ie convert 2/3 of Libdem voters.
- Get 23% out of 75% ie convert 1/3 of Tories and Labour voters.
Put in those terms, it's *obvious* that LibDems are the right tactical choice because of the huge pool of latent votes sitting with the Tories.