Where Can Romney Be Stopped?

Silver searches the electoral calendar for possible Romney upsets:

Losing Illinois on Mar. 20, or perhaps Maryland on April 3, could damage Mr. Romney. But there has been little polling in these states, and losses there would probably not have the narrative consequences that a loss in Michigan, Arizona or Florida would have. Then there are states like California and New York, which have a lot of delegates and where losses would be hard to excuse — but they do not vote until late in the process, at which point momentum might be of limited value.