John McCain hosted a barbecue last weekend and invited several potential running mates, signaling the opening of vice presidential candidate speculation season. Joining the presumptive Republican nominee at his Arizona home were Louisiana Governor Bobby Jindal, Florida Governor Charlie Crist, former Massachusetts Governor Mitt Romney, and former Arkansas governor Mike Huckabee.* All would be acceptable choices to a struggling GOP, but who will best help unite Republicans around the McCain campaign?

Like Democrats, Republicans are fractured this election season. The party that can quickly unite to claim moderate and undecided voters will boost its chances of winning in November.

McCain’s biggest weak points are his age, his economic policy, and his weakness with religious voters. Christian conservatives do not have an easily identifiable candidate this election season. Though McCain stands for many evangelical values, he does not trumpet his faith as Bush did in 2000 and Huckabee did earlier this year.

Bobby Jindal could provide McCain with the support he needs in the Christian community. Though Catholic, Jindal has appeal amongst evangelicals for his pro-family positions, including a hard line against all abortion. Mitt Romney received a mixed reception from evangelicals during the GOP primary, and could prove a liability for McCain on matters of faith.

However, Romney would bring McCain much needed business experience for his economic policy, and would give the GOP a clear heir apparent for 2012. Romney might also be able to bring in Michigan, providing much needed electoral votes, or at the very least force Romney is spend resources there.

Charlie Crist has been a popular first term governor and is widely rumored to be amongst McCain’s favorites. But a Florida news poll last week showed he might not bring as many Florida votes in the general election as first thought. Additionally, John Miller trashed Crist in a National Review article last month, pointing out the Florida governor’s pro-liberal past.

Another potential candidate is Mike Huckabee, though the politician-turned-comedian would not bring much to the ticket that Jindal or Crist couldn’t offer. Governors Mark Sanford (R-SC) and Tim Pawlenty (R-MN), along with Secretary of State Condelleza Rice have also been mentioned as likely candidates.

*CORRECTION: Mike Huckabee was invited to the gathering but didn’t attend, choosing an anniversary trip with his wife instead.