"Gun violence spiked — and arrests declined — in Chicago right after the Laquan McDonald video release." So reads the headline on a well-reported fivethirtyeight.com blogpost. McDonald was shot 16 times and killed by a Chicago policeman, an act that looks very much like police misconduct, and the release of the video, after Chicago Mayor Rahm Emanuel had been safely re-elected, got enormous attention in the city.

And apparently from police officers and from potential and actual criminals too. The article documents how the number of arrests declined and the number of homicides increased after the video was released. This is yet more evidence of what some have called a Ferguson Effect, of police refraining from proactive law enforcement and criminals shooting more victims, almost all of them black.

Another fivethirtyeight.com writer, Carl Bialik, has pooh-poohed the existence of such an effect, arguing that homicides have spiked only in some large cities and that the overall spike in the 60 or so largest cities was only [!] 16 percent — a thesis I criticized in earlier Washington Examiner blogposts. For more definitive analysis, see the Manhattan Institute's invaluable Heather Mac Donald, notably in this Wall Street Journal piece.

The Ferguson Effect and the alarming spike in criminal violence has not been a front-and-center issue in the presidential campaign, but it could become one. Bill Clinton speaking before jeering #BlackLivesMatter protesters made a point of defending his signing of the 1994 crime bill, and noted quite accurately that much of the demand for that legislation came from law-abiding black Americans who were tired of being victimized at incredibly disproportionate rates.

Clinton has since sort-of-apologized for speaking such uncomfortable truths, which are out of fashion with this cycle's Democratic candidates, including Martin O'Malley (who was booed by #BLM supporters for the heresy of saying "all lives matter"), Bernie Sanders (who yielded the podium to #BLM protesters who had initimidated him away from the mic) and Hillary Clinton (who concedes the #BLM's invalid contention that we are seeing an enormous trend toward white policemen shooting innocent black men).

Yes, there have been (though not in Ferguson, Mo.) nationally publicized and apparently unjustified shootings of black men, to which local officials (as in North Charleston, S.C.) have responded with prompt investigations and prosecutions. The shooting of Laquan McDonald appears to have been one such case, albeit not as promptly responded to. But the great danger here is not of racist police running amok but of police officers hanging back and black people getting shot and killed by criminals as a result.

We have seen this movie before, and the results are tragic — primarily for law-abiding black people. Bill Clinton appreciated this and responded to it in 1994. The crime bill he signed may have played only a minor role in reducing violent crime, much less than the police tactics championed by New York Mayor Rudy Giuliani and copied and adapted by mayors and police chiefs across the nation. And Bill Clinton seems to appreciate this again today.

But the Democratic party generally and Hillary Clinton in particular, whose popular vote majorities in primaries have come entirely or almost entirely from black voters, want to coddle the #BLM movement and indulge its misconceptions. That could be politically dangerous. Gallup reports that 53 percent of Americans now say they "worry a great deal" about rising rates of crime, up sharply from 39 percent in 2014 and the first time that percentage has been over 50 percent since 2001. The crime issue could start hurting Democrats again, as it did from the late 1960s until 1994, when Bill Clinton signed the crime bill that his wife and party are rushing to apologize for.