If you are reading this, there is a pretty high probability that you know Mexico has elections today for President, Deputies, and Senators. There seems to be no doubt that the formerly hegemonic PRI, which last ruled Mexico in 2000, will win. The question is, how big?
The presidency is elected by plurality, and so a voting result in the low/mid-40s will be good enough–as it was for Vicente Fox of the PAN in 2000. (The incumbent, Felipe Calderon, also of the PAN, won in 2006 with only around 36%.)
The Chamber of Deputies is elected by MMM. There are 300 single-seat districts elected by plurality, and 200 list seats determined by nationwide proportionality. ((Some sources mention regional districts in the PR tier. That is true, but only on the intra-party dimension: these districts, and the separate list each party presents in each district, matter only in determining which candidates take the list seats a party has won. They do not affect the total balance of seats among parties, which depends on the parties’ nationwide total votes.)) These seats are elected in parallel. That means that a party’s proportional share of the 200 is added to however many district seats it has won, with a partial exception to be addressed below. The votes cast for single-seat candidates are summed up to determine shares for list allocation, as there is no separate list vote.
In the Senate, there are three members elected from each state, and another 32 elected nationwide; again, the nationwide seats are in parallel and without a separate vote. In each state a party presents a (closed) list of two candidates. The plurality earns two, and the second party wins one.
The President and Senators are elected for six-year terms, the Deputies for three years. No one at any level can serve consecutive terms.
Will the incoming PRI president–assuming no huge surprise when the results come in–have a majority in either or both houses?
In the most recent Deputies election, in 2009, the PRI won just short of a majority: 237 seats (47.4%) on only 36.9% of the votes. The PRI was in pre-election (pri-election?) coalition with the Green Party (PVEM), and this combine actually did win a majority: 258 seats on 43.6% of the votes.
The 2009 result shows clearly that the system is MMM (parallel), not not MMP (compensatory) as some sources claim. A near-majority of seats for one party that wins less than 37% of the vote is pretty non-proportional! The one way in which the system is not purely parallel is that it includes caps on over-representation. No party may win more than 60% of the seats, or more consequentially, a seat percentage that is more than eight percentage points greater than its vote percentage.
It seems (though I am not sure) from the 2009 result that this provision is applied to a pre-election coalition, and not to such an alliance’s parties individually (–UPDATE–see Manuel’s comment—): the PRI’s own over-representation was more than 10 points. What matters, apparently, is the alliance, which was almost precisely at eight percentage points over-representation. Together in the nominal (plurality) tier the parties won 188 seats (184 PRI, 4 PVEM), which is 62.67% of the districts. (Oh, doesn’t plurality produce big distortions when there are three major national parties!) The parties’ combined votes, as noted, were 43.6%. However, there is a 2% threshold, so what really matters for the proportional-list seats is the “effective vote”: when below-threshold parties’ votes are removed, the two parties had 46.73%. That would earn them around 93 of the 200 list seats. This would get them to 281 seats. So, if my calculations are correct, the cap was triggered in 2009. ((I have said previously that it was not triggered at an election after 1997. Perhaps that was incorrect. The rest of this footnote is geared even more for anoraks than the main entry.
Maybe I am wrong here, rather than in my previous comments about the cap. That is, maybe the cap on over-representation is applied to individual parties, but is triggered only by comparing seat percentages with effective votes. If that is the case, the PRI, alone, did not trigger it, as it had 39.5% of the effective vote, and its total seat percentage won was then less than 8 points greater.
Maybe someone can clarify this arcane point!))
Will the cap be triggered in 2012? If so, will it affect the PRI’s chances of winning a majority? I would think it is likely to get a majority, as unless there is a great deal of ticket-splitting, the PRI should win over 42% of the vote. Winning 42% does not guarantee a majority of seats, but makes it likely. The party would have to win a sufficient number of district seats–about 167–to ensure the majority. However, even a small increase in the votes for the largest party should result in an even greater swing of seats in the PRI’s favor than the very large swing we saw in 2009 (when the PRI alone won 184). On the other hand, winning less than 42% of the vote makes a majority impossible–not counting votes and seats of alliance partners. ((The PRI is again in alliance with the Greens.))
Conclusion on Chamber of Deputies: A majority for the PRI looks likely.
As for the Senate, a majority depends on winning the votes plurality in many states, as well as a large enough share of the total nationwide votes. Given that the PRI currently governs about two thirds of the states, it obviously has the regional spread to pull this off.
Bottom line: a two-house majority for the new PRI president, Enrique Pena Nieto, looks likely, but not a sure thing.
Now, does this mean a restoration of the “old” PRI? Probably not, as the internal lines of authority in the party have changed, probably irrevocably. But that is a topic for another day…