“Our crime rate is going up,” former President Donald Trump claimed during the Republican National Convention last week, when he vowed to “Make America Safe Once Again.” Yet the most notable recent increase in the homicide rate happened on Trump’s watch, and violent crime has been falling since then. That gap between Republican rhetoric and reality corresponds with long-standing public perceptions of crime, which Americans routinely say is going up even when it is going down. Trump is hoping to capitalize on that misperception as he campaigns on a promise to reverse a nonexistent trend by “res…