The fatal shooting of 49 people at a Florida nightclub on June 12, 2016, is the latest in a long series of mass killings to restoke the national debate over gun ownership, with the Senate doing battle over the issue during the week after the tragedy.

The gunman in Orlando, Omar Mateen, was armed with a handgun and an assault rifle; in addition to those he killed, he wounded another 53, and he himself was killed by police.

The horrific attack — the biggest mass shooting in U.S. history — came less than six months after two suspects opened fire in a California social services center, killing 14 and injuring 21.

Despite the outpouring of grief and sympathy that followed the San Bernardino incident, though, the very next day the Senate rejected a bill to tighten background check requirements on would-be gun buyers — just as it did in 2013, shortly after a lone gunman killed 27 at Sandy Hook Elementary School in Newtown, Conn., including 20 children, six adults and himself.

Whether 2016 will be any different remains to be seen. In fact, the issue of how to strike a balance between gun rights and public safety has been a political hot potato for years, and one that Congress has dealt with gingerly — too gingerly, in the view of groups favoring tighter firearms regulations.

The political climate of 2016 would hardly seem auspicious for action on the issue; one of the presumptive presidential nominees, Republican Donald Trump, has called for Muslims to be temporarily banned from entering the country. Trump and President Barack Obama soon were engaged in a war of words, with Obamaattacking Trump’s proposals as “dangerous” not long after the president had made his 14^th televised statementfollowing a mass shooting since he was sworn into office. In that appearance, he called for tighter laws that make it harder to buy guns.

But Trump and other Republicans seemed to leave open a narrow possibility that some tightening of restrictions on who could get guns was possible as Senate Democrats mounted a filibuster.

A .44 caliber political issue

The last major piece of gun control legislation to make it into law was the assault weapons ban, which passed in 1994 as part of a larger crime-related bill approved by Congress and signed by then-President Bill Clinton. But the ban, which applied to the manufacture of 19 specific models of semi-automatic firearms and other guns with similar features, expired in 2004, and repeated attempts to renew it have failed.

Some Democrats thought their support for the assault weapons ban cost them control of Congress in the 1994 midterm elections. Whether or not that’s true, there’s little question that the politics of gun ownership have swung to the right. Republicans largely oppose gun control, and Democrats are split, with some lawmakers cautious about going against the views of more conservative constituencies, especially in rural districts.

That’s been true among the 2016 presidential candidates as well. Former Secretary of State Hillary Clinton, the Democrats’ presumed nominee, contrasted herself with Sen. Bernie Sanders of Vermont on the issue of gun control during their primary-season debates. And after 10 people died in a shooting at Umpqua Community College in Roseburg, Ore., Clinton promised shewould take executive action as president to expand background checks. Sanders, though historically more sympathetic to the gun rights cause, reacted strongly the day after the San Bernardino shooting with a series of tweets calling for universal background checks, closing the “gun show loophole” and renewing the assault weapons ban, among other proposals.

Gun money to 2016 presidential candidates*

Those measures would likely pass muster with the Supreme Court despite challenges that would surely follow based on the Second Amendment — “the right of the people to keep and bear arms.” In 2008, the justices struck down Washington, D.C.’s blanket ban on handgun ownership. The decision confirmed that individuals, and not just the police and military, have a constitutional right to own guns, but the ruling was a narrow one, applying only to a person’s right to keep a gun at home for self-defense. It didn’t imply that guns can’t be regulated in a number of ways.

Still, despite highly publicized mass shootings, no gun control measures have made it through the House and Senate in recent years.

That includes the so-called Manchin-Toomey amendment to require background checks in all commercial gun sales, including those at gun shows. The measure first came to a vote in April 2013, four months after the Newtown shooting. It failed, getting only 54 of the 60 votes it needed to overcome a filibuster. The Center for Responsive Politics found that nearly all of the 46 senators who voted against the amendment had accepted significant campaign contributions from the political action committees of gun rights groups. There were exceptions to the rule, notably the measure’s sponsors, Sens. Joe Manchin (D-W.Va.) and Pat Toomey (R-Pa.). But in general, the correlation was a close one.

No senators who were in office for the 2013 vote changed their position when the provision was brought up again after the San Bernardino killings in 2015. And the second time around only 48 votes of support for expanding background checks could be found. Another bill put to a vote that day, which was sponsored by Sen. Dianne Feinstein (D-Calif.) and would have prohibited individuals on the terrorism watch list from buying guns, was rejected as well.

The votes on Manchin-Toomey seem out of step with where the public stands. The Pew Research Center found in 2015 that 85 percent of Americans, including a majority of Republican respondents, support expanding background checks to include private firearms sales and purchases at gun shows.

Reflecting the opinion of many liberal political leaders, commentators and organizations, Feinstein said in a statement on Dec. 2 that Congress “has a problem — a debilitating fear of upsetting the gun lobby.”

Guns and money

There’s no denying that much of the strength of the leading gun rights organization, the National Rifle Association, comes from its broad and passionate membership base and its mastery of grassroots politics.

But if lawmakers seem to tiptoe around gun issues, it’s likely at least in part because the NRA and other gun rights groups are loaded for bear with a seemingly limitless stash of cash ammunition.

(For full data on contributions to candidates from gun control and gun rights interests, click here)

Gun rights interests have given more than$37 million to candidates, parties and outside spending groups since 1989, with 88 percent of the funds contributed to candidates and parties going to Republicans. And in the 2012 and 2014 election cycles, they let loose another $48 million (at least) in outside spending.

Top recipients of funds from gun rights interests, 1989-2016*

The NRA has provided the lion’s share of the funds, having contributed $22.3 millionsince 1989. During the 2014 election cycle, it further opened its coffers to make $27 million in outside expenditures.

Gun control groups, by comparison, have been a blip on the radar screen. They’ve given a total of $2.5 million since 1989; 94 percent of their contributions to parties and candidates have gone to Democrats.

But they did unleash $8.6 million in outside spending during the 2014 election cycle, nine times as much as they spent during the 2010 and 2012 cycles combined. Americans for Responsible Solutions, founded by former Rep. Gabby Giffords (D-Ariz.) and her husband, Mark Kelly, was behind $8.2 million of those independent expenditures. Former New York City Mayor Michael Bloomberg’s Everytown for Gun Safety spent $390,000.

Those figures don’t include $5.6 million in outside spending by Independence USA PAC, a super PAC backed by Bloomberg that hesays supports “candidates and causes that will help protect Americans from the scourge of gun violence, improve our schools, and advance our freedoms.” The money went to support federal candidates who were in favor of gun control and attack one who wasn’t; the group had 100 percent success rate. Bloomberg gave a total of $28 million to outside spending groups during the 2014 cycle, of which $17 million went to Independence USA PAC.

Top recipients of funds from gun control interests, 1989-2016*

Even greater than gun rights groups’ dominance in the realm of campaign finance is their superiority when it comes to lobbying Congress and federal agencies. In 2013 alone — right after Newtown — the gun rights lobby spent $15.3 million making its case in Washington. The following year, it spent $12 million, and in 2015 pared it to $11.4 million. The NRA accounted for $3.6 million of the 2015 number, but over the years, other groups — such as the National Association for Gun Rights, Gun Owners of America and the National Shooting Sports Foundation — have also made significant lobbying expenditures. And gun control groups? They spent just $1.9 million and under $1.7 million on lobbying in 2014 and 2015, respectively.

– Brianna Gurciullo/Viveca Novak, updated June