Answer: It depends.
It all comes down to the 106 voting members of the International Olympic Committee (IOC), who will decide on October 2, 2009, in Copenhagen.
Ultimately, victory hinges on securing roughly 49 votes, for the following reasons:
1. Invariably, owing to illness or schedule conflict, a few members will not be in attendance.
2. As is his custom, IOC President Jacques Rogge will not participate in the vote, save for a tie.
3. One member, former Samsung chairman, Lee Kun-Hee, is under status akin to suspension pending investigation of a slush fund corruption scandal in Korea.
4. Members (seven at the outset) whose countries are in the running are not permitted to participate in the vote.
Thus, it is estimated that 94-95 votes will be at stake in the first round of voting between the four finalist cities: Chicago, Madrid, Rio de Janeiro, and Tokyo.
In the first and second rounds, the key, of course, is merely to survive and thereby stave off elimination, because the lowest vote getter will be dropped and the voting will proceed to the next round until a city wins a majority of votes cast.
Every city's strategy is built around garnering enough votes to (a) survive the first round and then (b) pick up as many votes as possible from the eliminated city.
In Olympic bid-city elections, there is no "conventional wisdom," because IOC members' decisions are based largely on a personal calculus shrouded in secrecy and protected by the anonymity of the ballot box. Technical merit ratings are irrelevant because all finalist cities are deemed highly competent to host the games. While some have long espoused the virtues of geographic rotation, there is no evidence that the IOC abides by this theory. For the record, Brazil is the only country of the four in the running yet to host an Olympic Games (the USA hosted four summer games, while Japan and Spain hosted one edition each).
In the clubby environment that is the IOC, what really matters are the personal relationships between the IOC members and the principals of the respective bid cities, and secondly, geopolitics (in all its manifestations). Since personal relationships are not always what they appear to be, Chicago's fate lies in the USA's balance of favor as perceived by the aforementioned IOC members. In the positive column is the USA's improved global image owing to the popularity of President Barack Obama, and it is widely presumed that his presence in Copenhagen would provide a mighty boost to Chicago's bid.
On the other hand, the IOC leadership can hardly contain its contempt for the United States Olympic Committee (USOC) over its steadfast refusal to renegotiate lucrative deals that deliver 20% of worldwide Olympic sponsorship dollars to the USOC, which is just one of 205 National Olympic Committees. In addition, the USOC receives 12.75% of the $2 billion broadcast rights fee that NBC paid for the 2010 winter and 2012 summer games. To many IOC members, it is a symbol of American greed and arrogance that the USOC insists it should continue to receive a disproportionate amount of Olympic revenue. I believe the revenue-splits issue, more than any other, will end up being Chicago's Achilles' heel.
For what it's worth, here is my prognostication:
Round 1: Madrid eliminated
Round 2: Chicago eliminated
Round 3: Tokyo 53, Rio de Janeiro 44
Note to reader: Check back with me on October 2.