I am rather too preoccupied with the smoke and ash around the finca to have much to say here, but…
Elections for president and congress in Argentina are today.
The president is elected by qualified plurality: 45% suffices for a first-round victory, as does a plurality of between 40% and 45%, as long as the runner-up trails by at least 10 percentage points. There is probably no doubt that the next president will be the wife of the current Peronist one (Kirchner). Is there any chance of a runoff? Doubtful, I think. (There has not been a runoff since the current rules replaced an electoral college in 1995, though there should have been once: In 2003, the Peronists split and presented several candidates, but the number two candidate, former president Carlos Menem withdrew, and the runoff was never held. Nestor Kirchner became president on around a quarter of the votes.)
Argentina is the only country in the world to have staggered terms for its lower house (as far as I am aware). In each province, half the deputies will be elected today (plus or minus one in the case of odd numbers). Closed-list PR.
There are also elections for federal senators in some (half?) of the provinces. Closed-list plurality with limited nominations (i.e. two candidates nominated per party, with the plurality electing both and the second party electing its first-ranked candidate).
I hope some readers can fill in details or offer corrections in the comments. This is all off the top of my rather hazy head.
Fruits and Votes 
Snra Kirchner is ahead, may probably avoid a runoff – second-highest is only 23% or so.
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Why does Argentina have staggered terms for its lower house? The constitutional reform in 1995 did not go far enough. The stagger term for the lower house should have been abolished.
Does Argentina like most presidentalist systems in Latin America have U.S primary elections for party members to select who is there candidate for President? Was Ms. Kirchner just rubber stamped by her husband?
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You’re almost completely right, Prof. Shugart. Three senators are chosen for each province (i=24) with a limited vote (M=3, 2 seats for the plurality winner, 1 for the runner up). A third of the Senate is renewed every two years, in groups of 8 provinces. So, each district chooses Senators every six years, once in concurrent presidential elections and once during midterms in a 12 year period. The interesting peronist strategy is that its division in several provinces made it win the three seats.
Relating Suaprazzodi’s question, Argentina passed a bill that forced parties’ implementation of mandatory simultaneous primaries for national positions. It was never respected (by decree in 2002, just because Menem would have won Peronist competition and Duhalde would never allow it) and it was derogued by Congress in 2005. So, parties choose the candidate selection mechanisms they wish (mostly elites agreement at this time).
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Thank you for the additional information, Juan Pablo, especially on the Senate timing.
I would not call the senate eletoral system “limited vote” (or voto incompleto) as that is usually understood as a system in which voters vote for candidates (i.e., a variant of nominal, nontransferable voting), where the voter has more than one vote but fewer than M, and top M win. (M= district magnitude)
Of course, Argentina has a single list vote for Senate, and no candidate votes.
The lists, and thus the maximum seats a party may win, and not the voting, are “limited” or “incomplete.”
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Would ‘limited list’ of ‘fixed ratio’ be a better name for the ‘2 for the 1st an 1 for the 2nd list’ system used for the Argentinian senators? Is it the same system as used for the Bolivian and most of the Mexican senators?
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Yes, whatever we call it, it’s the same system as used for Bolivian and Mexican senators. And, to my knowledge, nowhere outside Latin America. (Maybe someone has better knowledge.)
(In Mexico, it is for 3/4 of the senators, as the other 1/4 are by nationwide closed-list PR, allocated in parallel. One vote.)
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