New post up on Guardian comment is free today on Cameron's inability to "unite the right."
Successful candidates reassure their base, then appeal to crossover voters to fill out a winning majority. In a US context, this is nicely staged in the primary process, with Democratic candidates angling leftward and Republicans to the right in order to secure their respective nominations, before turning back to the center for the general.
In the UK, the timing is not quite as clear, which may be what has tripped up David Cameron. He's waited to late to shore up support in the right-wing, and will now try to do it with loads of skittish moderates watching. Many of these centrists previously were not so interested in the campaign and would likely have missed the more hard-core overtures if they had been done last year or early in 2010.
Renard Sexton is FiveThirtyEight's international affairs columnist and is based in Geneva, Switzerland. He can be contacted at firstname.lastname@example.org