The Democratic primaries are generally proportional for the pledged delegates, but there is a 15% cutoff at the district level for district pledged delegates and at the state level for at-large pledged delegates, below which candidates do not get any delegates.

The California primary involves 370 pledged delegates and is held on Super Tuesday, February 5th. The latest poll for CA is Rasmussen 1/14 and has Clinton 38%, Obama 33%, and Edwards 12%. This leaves a rather large 17% undecided or other; let's split this proportionally among the three candidates, so now we have Clinton 45.8%, Obama 39.8%, Edwards 14.5% (rounding to the nearest tenth percent for convenience; rounding error makes the total add to 100.1% throughout the rest of the piece).

This is somewhat contrived because we've made it a 3 person race, and Kucinich will take a few percent or so (that same poll had him at 3%). The effect of this will only make it (slightly) harder for Edwards to meet the 15% criteria. Supposing now that these results also hold by district (which they very well might not), Edwards will not meet the cutoff to win any delegates. Then Clinton would get 370*45.8/(45.8+39.8) = 198 and Obama would get 370*39.8/(45.8+39.8) = 172 from that 370.

Now suppose that Edwards withdrew before Super Tuesday and endorsed Obama, and that the effect of this endorsements was to convince 75% of his supporters to vote for Obama while 25% switched to Clinton. Then Clinton would get 45.8 + 0.25*14.5 = 49.4% and Obama would get 39.8 + 0.75*14.5 = 50.7% -- the 370 delegates would now split Clinton 183 and Obama 187 (and Edwards the exact same zero). Under this scenario Clinton gets 15 fewer delegates and Obama 15 more -- that's a swing of 30 in the race.

If the effect of Edwards dropping out and endorsing Obama is to convince only 60% (rather than 75%) of his supporters in California to vote for Obama, the result would be Clinton 51.6%, Obama 48.5%, delegates Clinton 191, Obama 179; an overall win for Clinton but still a loss of 7 for Clinton and a gain of 7 for Obama compared to the three-way race, or a 14 delegate swing.

Just some numbers to think about =)