Donald Trump promised supporters in Texas that he would protect their right to bear arms in the wake of a massive shooting at a gay nightclub in Orlando, where 49 people were killed. (Reuters)

Even the National Rifle Association was uncomfortable with the way Donald Trump was talking about guns last week. The organization has worked hard to protect the rights of all kinds of people to bear arms, even opposing an effort last year to ban people on the terrorist watch list from purchasing guns. But when Trump suggested that people in nightclubs should carry guns for protection, he crossed a line.

"I don’t think we should have firearms where people are drinking," Wayne LaPierre, the association's vice president, told CBS on "Face the Nation" Sunday.

It is true that alcohol is a factor in a large proportion of homicides. Separating booze and guns would go a long way toward reducing violence, according to experts on public health and criminal justice.

"As a society, we’ve done a very poor job of managing the harms associated with alcohol," said Harold Pollack, a social scientist at the University of Chicago. "You really do want to keep alcohol and firearms separate."

According to a comprehensive federal study published in 1998, 39 percent of inmates in state prisons who were convicted of murder said they had been drinking at the time of the offense. (Not all murderers use guns, but a large majority do. In 2014, about 68 percent of homicides were committed with firearms, according to the Federal Bureau of Investigation.)

The researchers estimated median blood alcohol content for these offenders to have been 0.28 — suggesting they'd drunk the equivalent of about three six-packs of beer, on average, before committing the crime.

Later, LaPierre wrote on social media he meant that he had no objection to people carrying guns in bars and restaurants, as long as they didn't plan on drinking.

The combination of alcohol and firearms can be deadly regardless of who is drinking and who is carrying. Some people become more aggressive when intoxicated, which can result in a dispute getting out of hand, Pollack said.

More recent data from Illinois show that 39 percent of victims of homicides in the state between 2005 and 2009 died with alcohol in their system. By comparison, just about 10 percent were using cocaine and about 3 percent were using opiates.

People don't only drink in bars, of course, which makes segregating firearms from alcohol more complicated. If anything, the combination is even more dangerous in the context of violence at home. Among those inmates convicted of the murder of an intimate partner, the share who reported drinking when they committed the crime was even greater — 45 percent, according to the federal study.

"It’s hard to divide guns from alcohol in a country that uses as much alcohol and has as many guns as the United States," said Mark Kleiman, an expert on drug policy at New York University. Applied broadly, he pointed out, LaPierre's argument that there should not be firearms in the presence of alcohol suggests that people who drink shouldn't be able to keep guns in their homes.

Many states have laws against carrying guns while intoxicated, Kleiman said, but those are nearly impossible to enforce. He suggested barring anyone convicted of driving under the influence from purchasing a firearm. Generally speaking, only those convicted of felonies are disqualified, meaning that most people who drive drunk can still buy guns.

Other measures to get Americans to drink less in general, such as raising taxes on alcohol, would not only reduce violence but have additional benefits for public health, Kleiman said.

On Monday, Trump changed his previous position, writing that he meant that the club should have had armed guards, not that patrons should be carrying weapons.

"It's too bad some of the people killed over the weekend didn’t have guns attached to their hips where bullets could have thrown in the opposite direction," Trump had said previously.

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