I wrote in 2007 that it would be Madrid because of the old-boy network in the IOC. Old man Samarach was from Spain, his kid was running the Spanish Olympic Committee and fronting the Madrid bid, and they know how to twist arms while throwing a party. But the old boy may have overextended himself when he said, in so many words, "Vote for Madrid because I'd like to see it happen before I kick." So do you want to vote for an Olympics that might include a wake or one with naked beach volleyball?
Who votes for who isn't made public, but the vote seemed to go along continental lines in round 1, with Rio getting all the later support.
Round 1: Madrid 28, Rio 26, Tokyo 22, Chicago 18.
Round 2: Rio 46, Madrid 29, Tokyo 20.
Round 3: Rio 66, Madrid 32.
As Tip O'Neill said, "All politics is local." In Chicago, there's another saying: "We don't want nobody nobody sent."
This saves Chicago the headache of seven years of road construction followed by seven years of indictments.