An email:

In the last week McCain’s chances of getting the GOP nomination have declined considerably on Intrade while his chances of becoming President have remained relatively stable. One has to conclude, therefore, that either the immigration deal would help McCain in the general election by the exact amount that it would hurt him in the primaries, or that the political market hasn’t yet taken account of the effect the immigration deal has on the chances of McCain eventually becoming president. This is important because, under your formula, a candidate will come out doing better in the general election just by doing worse in the primaries, so long as his ultimate chance of becoming president doesn’t change.

I was wondering about that myself. We should see before too long.