Huck skipping. Jeb supposedly also skilling.
Sounds like they have seen insider polls and want to avoid embarrassing early low votes.
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Historically, however, the Iowa straw polls have meant very little. Only one non-incumbent has won it and the presidency in the last 50 years.
Santorum won it in 2012. Huckabee won it in 2008. Neither accumulated enough delegates to force themselves into a VP slot at a minimum.