WASHINGTON (CNN) - When the National Rifle Association talks, large swaths of Capitol Hill listen.
And when the NRA has aimed to block any new gun legislation in the wake of mass shootings, it's so far succeeded in thwarting such efforts.
So why does the group hold such sway?
Partly because more than half of congressional incumbents have gotten money and organizational help from the group, with many members having long-standing financial relationships with the NRA that date back years.
According to federal election data compiled by the nonprofit Center for Responsive Politics, eight lawmakers have been on the receiving end of at least $1 million in campaign contributions from the NRA over the courses of their careers.
Florida Republican Sen. Marco Rubio is among them.
And when 17-year-old student Cameron Kasky took the microphone at CNN's town hall on Wednesday night to ask Rubio if he'd refuse to accept further campaign donations from the NRA, the senator hesitated. Then he gave his answer: no, he wouldn't refuse.
His hesitancy shows how many in Congress have come to rely on the NRA's largesse to help them remain in office -- and their fear of crossing a group legendary for its ability to get its supporters out to vote.
While large industries such as defense, health care and finance give more to federal candidates, so-called "single-issue" groups have always been a bit different. For them, it's not necessarily as much about outspending and outflanking other industry powers as it is how they compare with the other side -- those advocating the opposite position.
By that measure, the NRA and its allies aren't just winning, they've been dominating for years.
In the 2018 election cycle so far, gun rights groups, including the NRA, have outspent the competition more than 40 to 1.
Gun rights groups have made nearly $600,000 in direct contributions and independent expenditures on behalf of congressional candidates, the data shows. Gun control groups? Barely $14,000.
Now watch this: When you look at the long-term relationships that gun rights groups have built with members of Congress, you find that nearly $13 million has flowed into congressional campaigns from the gun rights side over the course of current lawmakers' careers. From gun control advocates, by comparison, the figure just over $570,000.
The sheer breadth of campaign support provided by the NRA alone over the years helps explain just how deeply the organization is engrained in the election universe.
Among the 535 current members of Congress in both the House and the Senate, 307 have received either direct campaign contributions from the NRA and its affiliates or benefited from independent NRA spending like advertising supporting their campaigns.
Along with the eight current lawmakers who were on the receiving end of at least $1 million over their careers, 39 saw $100,000 or more in NRA money flow their way, while 128 lawmakers saw $25,000 or more.
The top senator on the list is North Carolina Republican Thom Tillis, with nearly $2 million, while in the House, Colorado's Ken Buck topped $800,000 in NRA support.
In fact, the data show that only six current Republican members of Congress have not received NRA contributions.
On the flip side, there are 24 Democratic members who have received support from the NRA.
The top Democratic recipient is 13-term Rep. Sanford Bishop, of Georgia's conservative 2nd District, who has seen about $50,000 in NRA support over the course of his career.
On his website, Bishop says he "promotes the values and morals of Southwest Georgians," which he says include guns. He also touts his "A+" rating from the NRA.
Disparity in lobbying efforts as well
When it comes to lobbying lawmakers and regulators, broader special interests like the defense industry, finance and health care, by contrast, spent considerably more than the NRA and its allies. Though those sectors are also much larger, with a myriad of interests.
According to the Center for Responsive Politics, the defense industry spent more than $126 million on lobbying in 2017. The financial sector spent half a billion dollars on lobbying in 2017.
But similarly to the campaign finance figures above, for lobbying on singular issues like guns, it's more about how you compare to the other side of your issue.
It's here that the leverage of the NRA and other gun rights groups becomes fully evident. While they spent north of $10 million last year, those advocating the opposite -- gun control -- spent less than one-fifth as much. The same is true going back at least five years.
In fact, gun manufacturing companies spent an additional $1.4 million on their own to lobby against new restrictions, on top of the $10 million gun rights groups spent.
Nearly as much as all pro-gun-control groups combined.
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