Some prominent nonprofits focusing on firearms are locked and loaded this election cycle, shelling out millions in hopes of influencing voters before they head to the polls Nov. 4.

This year, although gun control isn’t a major issue, groups on both sides support and oppose targeted candidates for the U.S. House of Representatives and U.S. Senate.

Gun control appeared to loom large for 2014 campaigns after the December 2012 massacre at Sandy Hook Elementary School in Newtown, Conn. According to the Gallup polling organization, support for stricter gun laws hit 58 percent in the following days — the highest since 2004.

However, that passion cooled. A poll last month from Gallup found that just 1 percent of Americans say gun control is the most important non-economic issue.

Public opinion hasn’t stopped gun groups on both sides from spending, though, as the chart shows.

[Article continues after chart.]

Infographic by Kelsey Harris

Infographic by Kelsey Harris

Some details on the groups and their spending:

National Rifle Association

So far, the National Rifle Association, the largest and best-known defender of the Second Amendment, has spent more than $19 million in congressional races, according to campaign finance records compiled by Open Secrets, a nonpartisan organization that tracks money in politics.

Among candidates it supports, the NRA has devoted the most money — $2.8 million — to Rep. Tom Cotton, R-Ark., who currently leads in his Senate race with incumbent Democrat Mark Pryor.

Among those it opposes, the NRA devoted more than $2.4 million to defeat Rep. Bruce Braley, D-Iowa, who is neck-and-neck in Iowa’s Senate race with Republican challenger Joni Ernst.

Americans for Responsible Solutions

The well-established NRA, however, has far outspent Americans for Responsible Solutions, the gun control group created by Gabrielle Giffords, the former Arizona congresswoman who was seriously wounded in a shooting spree while meeting with constituents at a shopping center near Tucson in January 2011.

Americans for Responsible Solutions has emerged as the leading spender among  gun control groups this election cycle, spending $3.3 million so far.

With a focus on House races, Giffords’ organization has contributed $373,572 to Rep. Michael Fitzpatrick, R-Pa. But it has spent much more — $1.2 million — against Republican candidate Martha McSally, who is seeking the 2nd Congressional District. seat in Arizona previously held by Giffords.

Independence PAC USA

Backed by former New York City Mayor Michael Bloomberg, Independence PAC USA focuses on stricter gun laws, improving education and advancing same-sex marriage.

Bloomberg’s group has spent close to $3 million supporting Democrats. Bloomberg himself, though, is the second-biggest individual donor this election cycle.

The former mayor has spent more than $11 million, with 96 percent of it to back Democrats. He has said he plans to spend $25 million more this month through Independence USA PAC.