Michael Brendan Dougherty explains the Huntsman campaign’s decision to run an attack ad against Ron Paul:

This attack ad signals that the Huntsman campaign no longer sees itself as vying for Mitt Romney’s spot, as the GOP’s preferred Establishment candidate, but sees itself as competing to be the next “not-Romney.” To do that, they have to stop Ron Paul.

Put another way, the Huntsman campaign has finally realized that its original strategy to try to supplant Romney where he was strongest was wrong. Huntsman’s plan all along was to focus obsessively on New Hampshire in the hopes of reproducing McCain’s 2000 and 2008 wins in New Hampshire, and this shift indicates that Huntsman has now recognized that this was a mistake. Unfortunately for Huntsman, he has the same problem in New Hampshire that Pawlenty had and Santorum now has in Iowa. Having devoted most of his resources to New Hampshire and having made that state the centerpiece of his campaign strategy, Huntsman cannot settle for a respectable second or third place showing if he wants to be considered as a viable candidate. As things stand right now, he might not even manage third place. This is the latest confirmation that Huntsman’s decision to run against Romney in the 2012 cycle never made any sense. At one point, it seemed as if Huntsman might have been in a position to undermine Romney in New Hampshire to make it harder for him to win the nomination, but Romney continues to hold a large lead despite Huntsman’s gains.

Jim Antle believes that Huntsman’s decision to target Paul makes sense:

It seems like an odd choice for Huntsman until you think about it: Huntsman is competing for Republican primary voters who are tired of a hyperinterventionist foreign policy but want a candidate less radical (or less conservative) than Paul.

If that were still true, I would agree that attacking Paul serves Huntsman’s interest, but the reality is that Huntsman lost almost all “primary voters who are tired of a hyperinterventionist foreign policy” once he took an ultra-hawkish position on Iran. War-weary voters would have to be out of their minds to support Huntsman, since he is only too ready to start a war with Iran while winding down the war in Afghanistan. Huntsman’s natural rival in New Hampshire and elsewhere at this point would have to be Gingrich, but Huntsman decided earlier this month to ally with Gingrich and shower him with compliments. Huntsman’s attack ad asks if Paul can be trusted, but Paul’s current and likely supporters already know that Huntsman can’t.