Nate Silver looks at presidential candidates who entered the race late. Jonathan Bernstein's take-away:
[Late entry] may hurt more in Iowa and New Hampshire than it does in early national polling. That makes sense; after all, the campaign looks a lot different in the early states than it does to the rest of us. If you're in California or Texas or New York, the campaign is mainly driven by "free media" coverage; debates loom large, and the press decides which candidates get the most air time. In Iowa and New Hampshire, however, voters are exposed to loads and loads of paid media and personal outreach by the campaigns, along with a local media environment that is heavily influenced by candidate campaigns.
The Dish 