16 year old comments aren't really very influential when working the effect someones opinion. More recent comments/actions will have to be pointed to. It seems that his Christianity is what gets the most air time and news print.
With 76.5% of Americans self identifying as Christian and only .7% as atheist it seems like a tough road to hoe to present that as a down side. Granted, few vote their theology, but at the same time few are going to alienated by his.
The honest weak spot Huckabee has might be a 'soft on crime' label that could have adhesion.
Huckabee is viable. And going from a third tier candidate to the front-runner speaks alot of not just his appeal (Paul has appeal too) but also points out his leadership/executive ability. Governors that have served multiple terms have proven executive ability. An initially obscure Presidential candidate moving past established front runners with larger budgets takes leadership ability.
His 2A stance is clearly positive, his recent glancing criticism of the Bush foreign policy without taking on the 'hate Bush' stank shows savvy as it precludes the expected 'just another version of Bush' tactic that the left will try to label the next Republican nominee. They will run against Bush (already are) and Huckabee showed that he has the political awareness to anticipate and counter political attack.
The 'easy kill' line is simple an attempt to worry supporters about his electability. The top 3 least qualified but most popular Democrats have much softer bellies. If they were to run Richardson or Biden they would have a better qualified and substantive candidate.
Iowa is 3 weeks away. If Huckabee carries Iowa it will be down to Huckabee, Romney, and Giuliani overnight. After super Tuesday we will likely have a presumed Republican nominee, as gun owners who is the choice here?
Hillary's wheels are coming off and she is 'reshaping' her campaign every week now so it is quite likely Obama will get the Democrat nomination. Even if Hillary does pull off a win, we have no good (D) to veto new gun legislation or pass repeals of current legislation should Heller be decided correctly.
Link to demographics cited. US Census citation at bottom of linked page.