Las Vegas shooting: Five reasons US gun control won't happen
In the wake of the mass shooting in Las Vegas, gun control advocates are renewing calls for tightening regulation on firearms.
If the story sounds familiar, it's because a similar dynamic has played out time and time again in recent years, after every new gut-wrenching incident of gun violence makes headlines.
On the federal level, at least, the interest and attention in new legislation has led to almost no action in decades, despite numerous polls showing widespread public support for measures like strengthened background checks and banning certain types of high-capacity gun magazines and military-style assault rifles.
With such a high death toll this time, perhaps the pressure for change will be greater. Here are five big obstacles that stand in the way.
The National Rifle Association is one of the most influential interest groups in US politics - not just because of the money it spends on lobbying politicians, but also because of the engagement of its 5 million members.
It opposes most proposals to strengthen firearm regulations and is behind efforts at both the federal and state levels to roll back many existing restrictions on gun ownership.
In 2016 the NRA spent $4m on lobbying and direct contributions to politicians as well as more than $50m on political advocacy, including an estimated $30m to help elect Donald Trump president.
Its overall annual budget is roughly $250m, allocated to educational programmes, gun facilities, membership events, sponsorships, legal advocacy and related efforts.
More than just the numbers, however, the NRA has developed a reputation in Washington as a political force that can make or break even the strongest politicians.
It grades politicians on their votes and directs its resources and those of its membership - both financial and organisational - to supporting its fiercest advocates and defeating staunch opponents.
As one former Republican congressman told the New York Times in 2013: "That was the one group where I said, 'As long as I'm in office, I'm not bucking the NRA.'"
Could it change? Gun-control groups, backed by wealthy benefactors like former New York City Mayor Michael Bloomberg, have become more organised in recent years, attempting to match the NRA's political might. As long as pro-gun groups keep racking up the legislative and electoral wins, however, they'll still be king of the hill.
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Most recent attempts to pass new federal laws regulating firearms are over before they ever really begin, stymied in the US House of Representatives, which has been in Republican hands since 2011.
In June 2016 a group of Democratic politicians staged a sit-in on the floor of the House to protest the Republican House leadership's decision not to hold a vote on two gun-control bills.
The House tends to have a pro-gun-rights tilt for the same reason it has recently tended toward the Republican Party in numbers larger than the pure national congressional vote total would indicate.
Due to the way the lines of House congressional districts are drawn, many by Republican-controlled state legislatures, there are more "safe" seats for Republicans than there are for Democrats.
In these congressional districts, the politicians are more responsive to their primary voters, who tend to be motivated by hot-button issues like gun rights. The price for crossing these voters is much higher than alienating those who, while perhaps more in favour of gun control, do not vote in Republican primaries.
Demographics also play a part in the pro-gun sentiment in the House, as there are more rural districts with higher levels of gun ownership than there are urban ones. Racking up big pro-gun-control majorities in urban areas does little to change this political reality in the House.
Could it change? Unless there's a flood of big-city liberals itching for the country life, demographics will be what they are. There have been some efforts to crack down on overly partisan gerrymandering, however. Barack Obama has made it one of his post-presidency goals, and the Supreme Court is currently considering a legal challenge to Wisconsin legislative districts that give a distinct advantage to Republicans. Getting politics fully out of line-drawing will be a tall task, however.
If a gun-control bill were to make it out of the House of Representatives, it would still face a challenge in the Senate, where the rural-urban divide plays itself out on the state level, as well. States dominated by big-city voters, such as New York, Massachusetts or California, are outnumbered by rural and Southern states with pro-gun sentiments.
The rules of the Senate can also thwart efforts to enact more stringent firearm regulation, thanks to the "filibuster" - a procedural hurdle that means most major pieces of legislation need the backing of 60 out of 100 senators to pass, rather than a simple 51-vote majority.
In 2013, following the Newtown, Connecticut, school shooting, it appeared that efforts to strengthen gun-purchase background checks had significant bipartisan support in the Senate. After a concerted lobbying effort by the NRA, however, the bill received only 56 votes in favour, four short of the mark necessary to break the filibuster.
No gun-control measure has come close to passage since then.
Could it change? Mr Trump has been perhaps the most vocal proponent of doing away with the Senate filibuster, as he views it as an obstacle to enacting his legislative agenda. A majority of senators are on the record against changing the rules, however.
With Congress more interested in rolling back existing firearm regulations than implementing new ones, left-leaning US states have taken a greater role in implementing gun-control measures.
After the 2012 school shooting in Newtown, Connecticut, 21 states passed new gun laws, including imposing assault weapons bans in Connecticut, Maryland and New York.
Some of the laws have run up against another barrier, however - the US judicial system. In recent years the Supreme Court has twice ruled that the right to own personal weapons such as handguns is enshrined in the constitution.
The Second Amendment says that "a well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed".
Gun-control activists point to the introductory clause as evidence that the amendment was meant primarily to create a "well regulated" militia. In 2008, however, a sharply divided court held that the Second Amendment provides a broad right to firearm ownership that prohibits stringent registration requirement for personal weapons.
Since then, lower courts have considered challenges to state-imposed assault weapon bans, registration requirements and open-carry prohibitions. So far the Supreme Court has declined to hear any of the new cases, however.
Could it change? Trump-appointed Justice Neil Gorsuch has made it clear he views Second Amendment rights broadly. The president is filling out the ranks of the lower courts with pro-gun-rights judges. If anything, the judiciary is moving to the right on this issue.
The enthusiasm gap
Perhaps the single biggest obstacle to new gun-control laws at the national level is that opponents tend to hold fiercely to their beliefs, while support for new regulation tends to ebb and flow around each new instance of violence.
The NRA's strategy, and that of pro-gun politicians, is to wait out the storm - to delay legislative efforts until attention turns elsewhere and the outcry fades.
Pro-gun politicians offer their thoughts and prayers, observe moments of silence and order flags flown half-staff. Then, in the quiet, legislative efforts are deferred and ultimately derailed.
On Monday, White House Press Secretary Sarah Huckabee Sanders told reporters "there's a time and place for a political debate, but now is the time to unite as a country".
Mr Trump, in comments as he left the White House for Puerto Rico, said "we will be talking about gun laws as time goes by".
As time goes by. As that song from the film Casablanca says, it's still the same old story.
Could it change? According to one poll during the 2016 presidential campaign, guns were an important issue for both Democrats and Republicans. That could be a reflection of that year's record-setting mass shooting in an Orlando nightclub or the first indication of a new trend.