By Lee Drutman and Alexander Furnas

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)

To better understand how a vote on gun control legislation might play out, we collected relevant data on 26 senators (19 Democrats, 2 Independents and 5 Republicans) who we saw as potentially conflicted on a gun vote. (For this, we include any Republican who didn’t get at least an A rating from the NRA, and any Democrat who didn’t get an F rating.)

As a start, we note that 40 Republicans either have an A or A+ rating from the NRA, and 34 Democrats get an F. We are pretty sure we know how these 74 senators will vote on any gun reform legislation. That puts gun rights supporters one vote away from the 41 votes they would need to filibuster any legislation. This is not a great starting point for advocates of gun control.

In order to assess how likely the remaining 26 senators might be to support gun control, we collected data on several additional factors we thought might be relevant to their vote. Our assumption is that the following things contribute to a higher likelihood of opposing gun control legislation:

• More contributions by gun rights groups to the senator in the senator’s last election (and fewer contributions to the senator’s opponent in that race).
• A lower Obama vote share in the 2012 election in the senator’s state.
• More registered firearm and “destructive device” dealers, manufacturers, importers and exporters per 100,000 residents in the senator’s state.

The more a senator’s value for one of these factors deviated from the average for our set of “swing senators,” the more weight we gave it in our overall score. By combining these factors into a single score, ranging from 0 – 10, we accounted for both senator specific influences (campaign finance, and NRA support), and state state level influences (partisanship, prevalence of gun business) on each potential vote.

These scores rank senators relative to other members in their party in regards to the various pressures they face on gun control legislation (we treat Independents Bernie Sanders (VT) and Angus King (ME) as Democrats, since they caucus with the Democrats)

The Democratic swing senator with a score of ten, Mark Udall of Colorado, is the most likely YEA vote, while Max Baucus of Montana, at zero, is the most likely Democratic NAY. On the Republican side of the aisle, Mark Kirk (R-IL) is the most likely gun control ally, while John McCain (R-AZ) seems the least likely to break with the Republican Caucus and support gun control. (Kirk is the only Republican Senator who has publicly supported an assault weapons ban)

Since our baseline assumption is that Republicans will tend oppose gun control, and Democrats will tend to support it, the scores we provide are not comparable between parties. A Democrat with a score of five and a Republican with a score of five are unlikely to have the same probability of supporting gun control legislation. Rather, we offer the scores as a way of comparing between members of the same party. Our scores are summarized in the following tables:

Democrats

Republicans

For all our underlying data and calculations, click here.

Let’s look at some of the key forces in more detail:

The Voters and the Gun Owners

Several of the Democrats on our list represent states where Mitt Romney won the popular vote, and where guns are prevalent. Several are also up for re-election in 2014. The scatter plot below helps us to identify these senators.

(graphic by Amy Cesal)

Here are the four Democrats up in 2014 who might face the most pressure:

• Max Baucus: Montana has 120 gun businesses per 100,000 people, highest in the country (according to ATF statistics). Only 41.8% of Montana voters supported Obama in 2012. (Tester, who just won re-election faces similar pressures)
• Mark Begich: Alaska has 104 gun businesses per 100,000 people.  Only 41.3% of Alaskans voted for Obama in 2012.
• Tim Johnson: South Dakota has 66 gun businesses per 100,000 people. Only 39.9% of South Dakotans supported Obama in 2012.
• Mark Pryor: Arkansas has 45 gun businesses per 100,00 people. Only 36.9% of Arkansans voted for Obama in 2012.

The Money

We’ve talked a lot about gun rights money. As we noted lasted month, almost half of the members of the 113^th Congress received NRA PAC money during their most recent race.

When it comes to our 26 senators, nine (Manchin (D-WV), Reid (D-NV), McCain (R-AZ), Baucus (D-MT), Rubio (R-FL), Tester (D-MT), Pryor (AR), Udall (D-CO), and Warner (D-VA)) have not received ANY pro gun money in the last six years. (We include ALL gun rights groups in this analysis. For a full list of gun rights groups we include, see our methodology at the bottom). In an additional seven states, however, there was gun rights money only supporting opposing candidates in the last election. And in four cases (Colorado (Udall), Montana (Tester), Warner (Virginia), and Nevada (Reid)) there was money on both sides.

What’s most notable is that in none of the 26 senate elections we looked at (which cover 52 candidates) were we able to find a senator receiving a single dollar from an gun control group. While the NRA exerts some tug on these cross-pressured senators, gun control groups have not made any effort to exert any financial pull in the opposite direction.

Data sources used: Influence Explorer, Opensecrets.org, and the Bureau of Alcohol, Firearms, and Tobacco.

List of gun control and gun rights advocacy organizations

Based on coding by the Center for Responsive Politics, we include the following groups as “gun rights” groups:

And the following groups as “gun control” groups: