Please note, this is all preliminary. A final count will not be known till at least Wednesday. But the IFE’s “PREP” (via the mirror site at Universal) shows the following as of around 8:00 a.m., Pacific Time today.

President, with over 96% of actas processed:

Calderon (PAN), 36.4%
López Obrador (PRD), 35.4
Madrazo (PRI), 21.5

There appears to have been a lot of ticket-splitting, and the current PAN vote shares for each of the congressional chambers rests at under 34%, while the PRI is around 28% and the PRD around 29%.

Nonetheless, a correspondent who has looked at the district-level results tells me that the PAN has won substantial pluralities in both chambers. The PAN has emerged as the most national of the parties, and the electoral systems of both chambers, while having a proportional component, are quite favorable to any party that has good regional spread. (More on this at Fruits and Votes.)

These relatively disproportional features of the Chamber and Senate electoral systems used to benefit the PRI. Now, with that party in third place, it is the PAN that is benefited by the plurality features of the system for congress. The PRD is somewhat over-concentrated (dominating the capital), and while this concentration has no negative impact on it for presidency (single nationwide plurality contest), it means that even if the PRD wins the presidency (still very possible), it will face a congress with up to 40% held by its main opponent and perhaps well under a third in its own hands.

The PREP results will be taken down Monday afternoon, and then we will have to wait for the full final count. This a real test for IFE, as the PRI may have had some opportunities in rural areas to pad the count for its congressional candidates. Not all polling places are monitored by the opposition. Can the PRI pressure poll-workers? I do not know. But it is not out of the question. Presumably the PRI, if it could pull it off, would prefer the more divided government under AMLO to Calderón and a strong PAN plurality. [UPDATE: Apparently the number not monitored is very small, so the concern expressed in this paragraph may not be so valid.--MSS]

I think Mexico’s electoral institutions are up to the challenge. But this is a big test.