In his speech last night, President Obama said the government should "make it harder for people to buy powerful assault weapons like the ones that were used in San Bernardino." In its front-page editorial on Saturday, The New York Times used stronger language, saying, "It is a moral outrage and a national disgrace that civilians can legally purchase weapons designed specifically to kill people with brutal speed and efficiency. These are weapons of war, barely modified and deliberately marketed as tools of macho vigilantism and even insurrection." On the same day, New York Times columnist Gail Collins agreed that "assault weapons," which she said "seem to be the armament of choice for mass shootings," should be banned. Hillary Clinton, the presumptive Democratic presidential nominee, concurs.
What exactly are these evil guns that are good for nothing but indiscriminate slaughter? Judging from their own words, Obama, the New York Times editorial board, Collins, and Clinton—like most people who support bans on so-called assault weapons—do not know what "assault weapons" are.
The president and the Times call the guns they want to ban "powerful," which suggests they fire especially large rounds. But caliber has nothing to do with the legal definition of "assault weapon," and AR-15-style rifles like those used in San Bernardino fire "low-caliber rounds that are less deadly than those used in many handguns," as theTimes itself noted in 2013.
Obama—who called the Bushmaster XM15-E2S used in the 2012 massacre at Sandy Hook Elementary School in Newtown, Connecticut, "fully automatic"—also seems to think "assault weapons" are machine guns. So does Clinton, who in 2008 advocated "sensible regulations" to keep "machine guns" away from "folks who shouldn't have them." Machine guns are already strictly regulated by the federal government, which since 1986 has banned sales to civilians.
The editorial board of the Times seems dimly aware that "assault weapons" are not machine guns, since it says they are "modified" (albeit "barely" or "slightly" modified) versions of guns used by soldiers. Likewise Collins, who correctly calls the guns she wants to eliminate "semiautomatic," meaning they fire once per trigger pull—unlike machine guns, which fire continuously, or assault rifles, which can fire either way. But Collins, who claims "semiautomatic weapons are totally inappropriate for either hunting or home defense," clearly does not understand how broad that category is, encompassing any gun that fires, ejects the empty casing, and chambers another catridge when you press the trigger. The semiautomatic weapons that Collins deems "totally inappropriate for either hunting or home defense" include many different models of hunting rifles and virtually all modern handguns except for revolvers.
Collins says "the San Bernardino murderers were wielding assault rifles, with which they were able to fire an estimated 65-75 bullets in rapid succession." Actually, the long guns used in the San Bernardino attack—a DPMS A-15 and aSmith & Wesson M&P15—were not assault rifles, which are capable of automatic fire. They were not even "assault weapons," according to California's definition. And Collins is wrong to think they fire especially rapidly. They fire exactly as fast as any other semiautomatic, which is about as fast as a revolver: as fast as you can pull the trigger.
Collins is also wrong when she says "assault weapons" are "the armament of choice for mass shootings." According to the Mother Jones tally of such crimes, handguns are by far the most commonly used weapon, accounting for 94 of 143 firearms used by mass shooters, or 66 percent. Only 20 of the guns, or 14 percent, would qualify as "assault weapons" under a 2013 bill proposed by Sen. Dianne Feinstein (D-Calif.). As Brian Doherty noted on Friday, "assault weapons" account for an even smaller share of all homicides. Rifles in general, which include many guns that are not considered "assault weapons," were used in about 2 percent of homicides last year.
Collins notes that "assault weapons...used to be illegal under a law that expired in 2004" and wonders, "If the law had stayed on the books, how many victims would have survived in San Bernardino, or at the elementary school in Newtown, Conn.?" We can say with some confidence that the federal "assault weapon" ban would have had no impact on either of those mass shootings, since it did not cover the guns used to commit them. Neither did the "assault weapon" bans of the states in which the massacres occurred, which were broader than the federal law.
Contrary to what Collins et al. seem to think, the "assault weapon" category has no reality independent of legislation. "Assault weapons" are whatever legislators say they are. 
Hence the rifle used in the Newtown massacre was not an assault weapon when the crime was committed but became one after Connecticut legislators approved a new, broader definition of the term. 
Similarly, the rifles used by the perpetrators of the San Bernardino attack are not assault weapons unless and until the California legislature decides to call them that.
The Times, which says "certain kinds of weapons...must be outlawed for civilian ownership"—by which it means not only that future sales should be banned but that current owners should be forced to "give them up"—is confident "it is possible to define those guns in a clear and effective way." But it does not propose a definition, presumably because such an exercise would make it obvious that the "assault weapon" label hinges on features, such as folding stocks, pistol grips, barrel shrouds, and flash suppressors, that make little or no difference in the hands of mass shooters or ordinary criminals, who in any case overwhelmingly prefer other types of guns.
In a 2014 essay titled "The Assault Weapon Myth,"   ProPublica reporter Lois Becket noted that these demonized guns are a "politically defined category" based on scary looks rather than criminal significance. "The law that barred the sale of assault weapons from 1994 to 2004 made little difference," she wrote. "It turns out that big, scary military rifles don't kill the vast majority of the 11,000 Americans murdered with guns each year. Little handguns do." Apparently the editors of the Times missed that essay, even though they published it. I guess they also missed the paper's own coverage of this issue, which has intermittently explained how arbitrary the definition of "assault weapon" is and notedthat AR-15-style rifles like those used by the San Bernardino murderers are among the most popular guns in the United States.
At this point—27 years after the Violence Policy Center's Josh Sugarmann recommended targeting "assault weapons" based on their "menacing looks," taking advantage of "the public's confusion over fully automatic machine guns versus semi-automatic assault weapons"—there is no excuse for continuing to parrot myths about the special murder-facilitating features of these firearms. Either Obama, Clinton, Collins, and her colleagues at the Times do not know what they are talking about or they are deliberately misleading the public. 
[This post has been revised to clarify that sales of new machine guns to civilians have been banned since 1986; possession of pre-existing weapons is still allowed, although strictly regulated.]