While signing executive orders at the White House on Aug. 25, President Donald Trump wrongly said that an 11-day span of no homicides in Washington, D.C., was the “first time that’s taken place in years,” a claim reiterated by other members of the administration who credited Trump’s federal takeover of the district’s law enforcement. An 11-day stretch with zero murders is rare in the city, but there was a 16-day period with no murders earlier this year, from Feb. 25 to March 12, according to...