The outcome of tomorrow's vote in West Virginia is not in doubt, and neither is the impact it will have on the nomination process, which will be commensurate with its 0.9% share of pledged delegates.

So to make things interesting, the number I'll watch is percentage of each candidate's voters who say they plan to vote for John McCain in November regardless of who wins the nomination.

This assumes that the exit poll will have the same questions as it did in Indiana and North Carolina, where voters were specifically asked who they planned to vote for in November, regardless of how they voted during the primary.

The fact that West Virginia is a semi-closed primary (Democrats and unaffiliated voters can participate, but not Republicans) is largely irrelevant -- just under 70% of West Virginia voters are eligible to vote.

In North Carolina, which also had a semi-closed primary, 16% of Clinton's voters said they planned to vote for McCain even if she won the primary. (Oddly, in Indiana, which is open, 13% of her voters said the same.)

Assuming the exit poll has the same question, I'll set the over-under at 15% for the percentage of Clinton supporters who will vote McCain even if she wins the nomination, and I'll set the over-under at 4% for Obama.