AMERICA HAS endured more than one mass shooting per day so far this year, according to the Gun Violence Archive, a non-profit research organisation. This weekend, the country suffered two more. The carnage started on the morning of August 3rd, when a man armed with an AK-47 killed 20 people in El Paso, Texas. Hours later, a man outfitted with body armour, an assault rifle and a handgun killed 10 people in Dayton, Ohio. After such events Democrats often call for stronger gun-control laws; Republicans recommend reforming the country’s mental-health system or banning violent video games. Finding common ground has proved almost impossible.

Polls suggest that Americans tend to favour the Democrats’ approach. According to a survey conducted in March 2019 by the Associated Press-NORC Center for Public Affairs Research (AP-NORC), 67% of Americans support stronger gun laws, up from 55% in October 2013; 10% think they should be relaxed (down from about 14%); 22% think the existing gun laws should be left alone (down from 28%). Roughly 60% of Americans think military-style semi-automatic weapons, of the sort used in this weekend’s shootings, should be banned outright.

Yet Congress has not passed meaningful gun-control legislation in 25 years, for at least two reasons. First, gun enthusiasts are fervent about their cause. According to the AP-NORC poll, gun owners are far more likely than those who do not own guns to contact public officials about gun policy or donate to either pro- or anti-gun organisations.

Second, polarisation has led to legislative gridlock, and mass shootings make things worse. A paper by David Barney of the University of Massachusetts Amherst and Brian Schaffner of Tufts University, finds that after mass shootings public opinion becomes more polarised. Using data from the Cooperative Congressional Election Study, a bi-annual survey administered by Harvard University, the authors show that living within 25 miles (40km) of a mass shooting causes Democrats to become about 2 percentage points more supportive of gun control, on average. Republicans become about 2 points less supportive.

On August 5th President Donald Trump tweeted his support for bipartisan gun-control legislation. “Republicans and Democrats must come together and get strong background checks,” Mr Trump wrote. This is not a new idea, and may not get very far. In the wake of the Sandy Hook Elementary School shooting in Newtown, Connecticut, in 2012, in which 26 people were killed, the Senate voted on a bipartisan law that would have required background checks on all commercial gun sales. It was defeated by a vote of 54 to 46. Since then, there have been more than 2,000 mass shootings in America.