HECKLING politicians is rarely an effective form of advocacy. In the midterm elections advocates for illegal immigrants heckled Barack Obama—and mostly were shouted down. But at a series of recent political events, protesters standing up to shout that “black lives matter” have been causing ripples in the Democratic presidential-primary race. “We are in a state of emergency,” declared one protester at Martin O’Malley, a presidential aspirant and former governor of Maryland, at the annual Netroots Nation conference in Phoenix in July. When he responded that “All lives matter,” he was summarily booed. Bernie Sanders, a Vermont senator and Congress’s lone self-described socialist, initially refused to “out-scream people” and simply pointed to his record on civil rights (he marched with Martin Luther King junior in the 1960s). But this only inflamed protests further. At another event Sanders supporters tried to shout down the heckling with the phrase “We stand together”—a strategy that a writer at Time magazine described as the “worst idea in the campaign’s short life”. Mr Sanders has since shifted gears and met with activists. On August 8th in Keene, New Hampshire, Hillary Clinton discussed criminal-justice reform with five “Black Lives Matters” protesters who had failed to make it past security at the event she was hosting. The Black Lives Matters campaign is plainly getting results.

It is hardly surprising that criminal-justice reform should feature heavily in the Democratic primary. It is right that Mrs Clinton, whose husband introduced one of the toughest crime bills in recent American history, and Mr Sanders, who represents a largely rural and white state, should be probed for their take on evidence of institutional racism within America’s criminal-justice system. Without that pressure, Mrs Clinton might not have made prison reform the topic of one of her first major speeches since declaring.

Lack of trust in police forces is contributing to a spike in murder rates But looking at the Black Lives Matter campaign in detail raises some worrying queries. For example, on its website, the group claims that “every 28 hours a black man, woman, or child is murdered by police or vigilante law enforcement.” That is a deeply questionable claim. According to the Washington Post, which is running a tally, 155 black people have been killed by police so far this year—out of 607 total. That is not quite one every 28 hours—but no matter. What is important, however, is that less than a tenth of this total was unarmed, 24 of whom were black. So to state that every black person killed by a police officer in a country as violent as America is “murdered” is inaccurate. Sure, 155 people killed by police is too many, and 607 is a problem, but of those who were black 85% were armed. The view that police officers are mostly murderers, however, runs through the site. On the “National Demands” page, for example, the campaign calls for the "immediate arrest" of Darren Wilson, the police officer who shot and killed Michael Brown in Ferguson, Missouri, last year. This despite the fact that a grand jury decided not to prosecute him. There are reasonable arguments to be made about biases within the grand-jury system, but jurors have decided there is not enough evidence to prosecute Mr Wilson. Throwing out the rule of law over frustration with a particular decision is a dangerous way to win reform. Another Black Lives Matter demand is for a “decrease in law-enforcement spending at the local, state and federal level” and “a reinvestment of that budgeted money into the black communities most devastated by poverty.” There are legitimate complaints to be squared at the culture of certain police departments, which are often more confrontational than necessary with certain demographics, particularly those who are poor and black. But it bears mentioning that many of these same poor, black people desperately need the police, too. It should not be considered a right-wing talking point to note that far more black people are killed by other black people than by police officers. Baltimore alone has had over 200 murders so far this year—almost all of young black men. What black people in cities such as Baltimore and St Louis need isn’t less policing. It is better, less institutionally-racist, less thuggish policing that actually solves crimes. If so many murders didn’t go unsolved, then perhaps there would be fewer of them.