I guess if we can say this, then we also have to say Bill Clinton caused a severe drop in crime in the U.S.?
Slick Willie's not the only recent U.S. President...
But note that the long downward trend in homicides and other violent crimes in this country coincided with a long period of relative economic prosperity, as well a period of expansion of the right to keep and more importantly bear arms, to where shall-issue concealed carry laws are the norm rather than the exception.