http://www.desmoinesregister.com/story/news/elections/presidential/caucus/2015/05/12/jeb-bush-skip-iowa-straw-poll/27187589/Bush is trailing Walker in Iowa and is quickly losing ground to Rubio and Cruz, and he announced yesterday he'll skip the meaningless straw poll. He's pretty much completely neglected Iowa so far and has understandably gotten killed by the state press since they their first-in-the-nation caucus status seriously (way too seriously). After he made headlines for flubbing a question on whether he'd have invaded Iraq in 2003 if he knew then what we all know now (he answered yes and was promptly ridiculed), Bush announced months in advance he'd skip this meaningless exercise.
The straw poll is nothing but a money trap and it's bankrupted a lot of candidates over the years, but Bush's precarious standing in Iowa probably necessitated an investment just so he doesn't finish way back in 5th place and end up getting even more negative press for it. The greatest threat to Bush is allowing a fringe-acceptable candidate to catch fire in Iowa, finishing in the top 3 in New Hampshire, and then romping in South Carolina to become a legitimate candidate in the eyes of GOP primary voters.
Bush needs to spend that $100 million he'll raise this month by bending flimsy super PAC rules somewhere, and it probably should have been Iowa.