A new poll out from Public Policy Polling this afternoon, which gives President Obama a 3-point lead over Mitt Romney, tests the effect of potential VP picks on Romney's chances in November:

In addition to looking at the head to head between Obama and Romney we also tested to see how some different potential GOP running mates might affect the ticket. Four of the people we tested-Jeb Bush, Chris Christie, Mike Huckabee, and Rick Santorum- slightly improve Romney's numbers against Obama. And four of the people we tested- Sarah Palin, Ron Paul, Marco Rubio, and Paul Ryan- slightly hurt Romney's numbers against Obama. In only one case- Palin's- does the introduction of a running mate make more than a 3 point difference in how Obama and Romney match up.

The running mate who helps Romney the most- allowing him to achieve a 47/47 tie with Obama- is Christie. In contrast to Romney, Christie actually has positive national favorability numbers at 36/34. Christie's inclusion doesn't have a big impact with Democrats or independents but it helps Romney shore up the party base, going from an 82-10 lead with Republicans to an 86/9 one.

Jeb Bush gets Romney to within a point of Obama at 48-47 and Mike Huckabee and Rick Santorum both pull him to within two at 48-46. The main positive effect any of those folks has for Romney is helping to shore up the GOP vote. Bush gets him up to 85%, Huckabee to 84%, and Santorum to 83%.

Then there are the potential VP's who hurt Romney- if only slightly. Ron Paul as running mate expands [Obama's] lead to 4 points at 48-44, Paul Ryan ups it to 5 at 48-43, Rubio to 6 at 49-43, and Palin to 7 at 50-43.