Chicago's bid for the 2016 Olympics was widely perceived to be a frontrunner but was eliminated in the first round of voting. Fractured relationships with influential IOC members and a "go it alone" attitude among American Olympic leaders of the time are believed to have doomed Chicago's bid.
Blackmun and his team have said they will not submit a US bid until they're comfortable America has the international relationships neccesary to succeed.
The decision not to bid for the next available summer games ensures it will be at least 20 years between Olympics held on US soil.