As the Senate prepares to take up the first major gun control debate since last December's shooting massacre in Connecticut, a Sunlight Foundation analysis of the political pressures on 26 key senators paints a pessimistic picture for passage. Absent a major pressure campaign to push senators to support gun control legislation, the political calculus points against the Senate passing any reform.

The infographic below details the various pressures senators face on a gun control vote. We've collapsed the factors into a single Gun Reform Index, where 10 is most likely to support gun reform and 0 is least likely. The index ranks each senator relative to other key senators within their own party. More details and explanation follow the graphic.

(graphic by Amy Cesal and Alexander Furnas)

The tragedy at Sandy Hook Elementary has brought gun policy back to the forefront of our national conversation. As a nonpartisan, nonprofit Sunlight takes no stance on the issue, but we have put together a collection of resources looking at the legislation, policy and influence around gun rights and gun control, plus the groups and lawmakers involved.

The Gun Lobby

Sunlight Foundation Senior Fellow Lee Drutman reviews the political influence of the National Rifle Association and the leading gun control group, the Brady Campaign to End Gun Violence. Read his full analysis in this blog post.

Lee notes that when it comes to the debate on gun policy, Congress is pretty much only hearing from one side. The NRA spends 66 times what the Brady Campaign spends on lobbying, and 4,143 times what the Brady Campaign spends on campaign contributions. Since 2011, the NRA spent at least $24.28 million: $16.83 million through its political action committee, plus $7.45 million through its affiliated Institute for Legislative Action.

According to Influence Explorer records, the Brady Campaign spent $5,800 this election cycle and reported $60,000 in lobbying costs.